Since the 1960s, the United States government has been shooting lasers at the moon. No, this is not a covert government conspiracy or a relic of the Cold War. It is NASA’s attempt to prove Einstein’s theories right.

Let me explain.

A little over 100 years ago, Albert Einstein published his theory of general relativity, a set of physical laws that upended our understanding of how gravity works. He suggested that time and space are connected, and that large masses (such as the Earth) could distort both of these dimensions. While comprehensive, the theory still had to be tested, to establish its validity and to understand its nuances in the real world.

About 50 years later, NASA went to great lengths to make this happen. The Apollo program sent astronauts to the Moon between 1969 and 1972, and while they were there, several astronauts left refractors (basically large mirrors) on the surface. These mirrors enabled astrophysicists down on Earth to use them as reference points for studying the distance between these two bodies, a technique called “lunar ranging,” yielding data that could be used to study Einstein’s theory of general relativity.

What does the distance between the Earth and the Moon have to do with Relativity? Well, lunar ranging lets astrophysicists understand every minute detail of the Moon’s orbit around the Earth, letting them test Einstein’s theory about how gravity works against how it actually does. If astrophysicists tried to calculate what the Moon’s orbit should look like based on Einstein’s theory, and their calculations turn out to not match what actually happens, Einstein’s theory is probably incomplete. But if they run their calculations and it turns out they did correctly predict how the Moon actually orbits the Earth, this suggests that Einstein may have been onto something.

How does lunar ranging work?

The lunar ranging technique that astrophysicists use to measure Earth’s distance to the Moon is very similar to sonar. With sonar, submarines bounce sound waves off neighboring ships and measure how long it takes for the sound to return. The time delay indicates the ships’ distance away. Astrophysicists use a similar technique with lunar ranging, but they don’t use sound waves – they use light.

The researchers start by aiming a large laser pointer at a refractor on the moon and sending out a very short pulse of light. The light only stays on for one tenth of one billionth of a second, long enough to produce a stream of light that’s about one inch long. Then, at 671 million miles per hour, the light travels to the moon, bounces off a refractor, and hits a receiver back on Earth. The whole process takes about two and a half seconds. By calculating the exact amount of time it took the light pulse to make the round trip, researchers can determine the distance between the laser pointer and the refractor on the Moon.

Finding a Fixed Distance

Astrophysicists in the United States and the Soviet Union started bouncing light off the Moon in 1962, before the refractors were in place. However, their measurements were not that precise. These astrophysicists were really interested in measuring the distance between the center of the Earth and the center of the Moon, but since light doesn’t travel through the moon, all they could do was measure surface to surface. There was no way they could directly measure how long light takes to get to the middle of the Moon.

They determined that they could overcome this limitation by calculating the exact distance from the surface of the moon to its center. But since they were not aiming at anything in particular at the time, their lasers could have bounced off anything — from a mountain to a canyon to a small bump on the surface of the Moon — meaning there was no way to really know the true distance between the surface and the center. It was not until astronauts put the refractors in place that the moon’s distance could be measured with precision. The refractors never move, which means they will always sit at a fixed distance from the moon’s center. So, there’s no guessing what that extra distance will be.

Interestingly, it’s not as easy to establish a fixed point here on Earth. Ideally, the receiver should be at a fixed distance from the center of the Earth, just like the reflectors are to the Moon’s center. But the Earth’s crust is always moving – from changes in atmospheric pressure to shifts in the tectonic plates to tides from the sun and moon — the surface of the Earth rises and sinks on a regular basis. Physicists have to pay attention to these factors and account for them in their calculations to determine the true distance between the centers of the Earth and Moon.

With the refractors in place and the Earth’s movements known, astrophysicists can estimate the distance between the Earth and the moon within two centimeters!!

(NOTE: I’ve been trying to think of something more Earthly to compare this to, but there is no comparison. The Moon is 238,900 miles away. And astrophysicists can estimate the Moon’s distance within less than an inch. Imagine that!)

Why Do This?

Isaac Newton established the first theory of gravity – he suggest that all massive objects attract other massive objects, and that the strength of this attraction depends on 1) the distance between the objects and 2) how massive they are, relative to each other. For instance, everything falls downward on Earth because our lives take place on or near the surface of the Earth, and really far away from other massive objects such as the Moon, Mars, and Venus. These other bodies are pulling on us (the Moon, for instance, pulls water up to create tides), but overall, the Earth, by far, has the greatest pull.

Newton’s theory of universal gravitation suggest that gravity always pulls things in a straight line. But Einstein’s theory of general relativity suggested otherwise. He suggested that gravity bends space: that gravity curves around massive objects, and that space and time actually grow and shrink in the presence of gravity. We used to think that a meter is always a meter long, and that second is always be a second long, but Einstein showed that these constants that we take for granted are not that constant.

This phenomenon does not affect our everyday lives, where everything happens on a relatively small scale in both space and time. But it is easier to see these effects on objects that are farther from the Earth and move at very high speeds relative to us, such as the Moon. This is why NASA went to such elaborate lengths to study Einstein’s theory – they couldn’t see its effects by studying anything here on Earth.

What’s another example of where we see the effects of relativity? The artificial satellites that orbit in the upper reaches of Earth’s gravitational field. In fact, engineers need to understand relativity to be able to measure our exact position on Earth with GPS. This means companies like Google and Apple depend on NASA’s lunar ranging experiments.

Global positioning systems and relativity

GPS consists of a network of 24 satellites that all talk to each other and depend on very precise timing and knowledge of their own locations relative to you to accurately estimate your location. The satellites are arranged in orbits such that at least four satellites are visible from any point on Earth at any time, and each satellite has a clock on it that measures time to the nanosecond (one billionth of a second).

Now, imagine you’re driving through an unfamiliar neighborhood, trying to find your way to the highway to bring you home, and your GPS is on, faithfully tracking your location. The GPS in your car is talking to those four satellites in the sky, determining where they are and how long it takes to receive a signal from each one. From this information, similar to how we triangulate location using phone towers on the ground, your GPS device estimates your location.

Since your car is talking to satellites so far up in the sky, though, the effects of special relativity kick in and affect your GPS’s ability to accurately measure time. Special relativity suggests that, for objects moving at high speeds relative to the observer (such as a satellite compared to a person on Earth), time slows down. As a result, the clocks in GPS satellites, which are orbiting at about 8,700 miles per hour, actually fall behind the clock in your GPS device by 7 microseconds (seven millionths of a second) per day.

On top of this, these satellites’ distance from Earth also affects how they experience time. Massive objects like Earth stretch space-time, such that time takes longer to happen near the Earth. But as you get farther from Earth, the planet’s influence on space-time diminishes, and time speeds up. Consequently, GPS satellites, which are travelling about 12,500 miles above the ground, get ahead of Earth time by 45 microseconds per day.

Adding all of that up, the clocks on GPS satellites move faster than the clock in your GPS device in your car by about 38 microseconds per day.

If engineers did not take these relativistic effects into account when they designed your GPS, it would give you a false reading after only two minutes, and these errors would accumulate to about six miles a day. That’s not very useful if you’re trying to find your way home!

What does this have to do with shooting lasers at the moon?

As the GPS example demonstrates, physicists need to understand exactly how gravity works to develop new technologies that are affected by general and special relativity. As I described earlier, the moon’s orbit is a great system for testing theories of gravity against. If we understand the moon’s orbit, we can test whether a theory of gravity, such as Einstein’s theory of general relativity, fits what is actually happening in space. By fine-tuning Einstein’s theories, we could potentially develop GPS devices that can calculate your position not just to a few feet, but to the inch!

Ben Marcus is a public relations specialist at CG Life. He received his Ph.D. in neuroscience from the University of Chicago. You can follow him on Twitter @bmarcus128.

What does this…

…have to do with this?

The answer lies in these tiny organisms:

When we think of milk, we usually think of cows, but by definition, all mammals produce milk. Mammals lactate, or secrete milk, that is unique to each species and contains a mixture of fats, proteins, and some carbohydrates. Milk from several of those mammals, including cows, buffalo and goats, is used in a wide variety of foods: it’s steamed for your pumpkin spice latte, churned to make butter, and whipped and frozen to make ice cream. But by far one of milk’s most common and versatile products is cheese.

Cheese is made out of milk’s two major components. Little Miss Muffet knew all about them – curds and whey. These components form when milk curdles, which happens when someone adds an acid (like from lemons or vinegar) to it. The solids (mostly fat and a protein called casein) turn into lumps called curds, while the remaining liquid (a mixture of different proteins suspended in water) is called the whey. While whey can be used to make certain cheeses such as ricotta, it is the curds that cheesemakers prize as the ultimate base for cheese.

There are several wheys – oops, I mean ways – to make the milk acidic so that it will curdle. Someone can manually add acid, such as vinegar or lemon juice, to it, as is done to produce queso fresco and paneer. More often, however, cheesemakers go a more scientific route: they use bacteria.

Most of the time, cheesemakers use a natural bacteria in milk called lactobacillus to eat milk sugars such as lactose and secrete lactic acid. Lactic acid builds up, causing the milk to curdle. (This process happens in your refrigerator, too – have you ever left a gallon of milk in the back of your refrigerator for a bit too long and found a lumpy, gooey mess? Blame lactobacillus.)

Other bacteria in milk cause lactic acid to build up as well, including lactococcus and streptococcus bacteria. Swiss cheese uses a bacteria species called propionibacter, which exhales carbon dioxide (just like us!) and leaves behind holes in the cheese. Each type of bacteria has unique by-products that affect the final texture and taste of the cheese.

While cheesemakers use tiny bacteria to make lactic acid from milk sugars, they also make curds using a compound found in cows. Cows’ stomachs naturally produce a mixture of enzymes called rennet. Cheesemakers use rennet to process the milk protein casein. The enzyme mix chews up the casein, causing it to lump up and curdle into the curds.

Once you have curds, you can make all different kinds of cheeses. Curds initially feel like a soft gel, which is perfect for making soft cheeses. To retain this texture, soft cheeses are almost immediately drained and salted, then packaged and sold. Cheesemakers make harder cheeses by heating curds. Heat not only evaporates the whey and makes the cheese less gel-like, it also affects the cheese’s taste by changing the chemistry of the bacteria culture in the milk. Cheesemakers typically add salt to preserve the cheese, but this salt also has a second function – it draws whey out. A cheesemaker can also change a cheese’s texture by stretching it (for example, mozzarella) or by washing it to make the flavor milder (for example, gouda and Colby).

Finally, once the cheese is made, cheesemakers use bacteria to ripen it. Like wine and scotch, cheeses can be aged for years! The remaining microbes in the curds break down the proteins, fats, and carbohydrates in the curd very slowly, which affects the cheese’s texture and taste. Cheesemakers let these bacteria do its work in carefully controlled environments so the cheese doesn’t spoil, and after months or years, the final product yields rich and varied tastes.

What’s in store for the future of cheesemaking? As you might have guessed, research scientists can use their knowledge of microbiology to make new and exciting cheeses for us to try. This is already happening in the underground bunker at Jasper Hill Farms. There, the Kehler brothers have started a microbiology lab dedicated to finding the perfect blend of bacterial species for their cheeses. You can read more about them here: https://www.nytimes.com/2017/02/06/dining/jasper-hill-farm-cheese-science.html.

The next time you next sink your teeth into some deep dish, think about all the bacteria that have worked so hard to bring that tasty cheese to your tongue.

Stefanie Kall is a Ph.D. candidate in biochemistry at the University of Illinois, Chicago.

Sugar is everywhere. Kids crave it, pastry chefs live by it, and dieters avoid it like the plague.It comes naturally in our fruits, it’s added to our drinks, and it’s found in some form in virtually every packaged item at the grocery store. Some of us live by it, and for many of us, it does not love us back. But no matter what you say about it, sugar and its relatives are important for our health and well-being. Despite the bad rap that sugar has acquired over the years, sugar is actually critical for our survival for two reasons: it motivates us to eat and 2) it gives us the energy we need to get through most of our day.

First, why does sugar motivate us to eat? Its simple. “Sweetness” is the taste that, in its purest sense, tells us that the food we are eating has nutritional value. Without it, our evolutionary ancestors would not feel any inherent reason to try new foods, and they’d never find the ones that would fill them up. This function of sugar is precisely why we have evolved to enjoy the taste of sugar – its sweet taste encourages use to eat foods that will provide us with energy.

This is where sugar’s second benefit comes in – it gives us the fuel we need to make it through the day. Breakfast is dominated by carbohydrate-filled goodies like cereal, toast, and pancakes because carbs (the base components of sugar) are filled with energy. While fats contain more energy, sugars are more easily digestible. In fact, there is an enzyme in your saliva, called salivary amylase, that starts digesting the sugar in your food while it is still in your mouth! Since sugars are so important, you better believe our bodies are always at the ready to accept them.

The Science of Tasting Carbs

Our tongues are excellent at detecting simple sugars like single glucose molecules. In fact, our mouths contain a specific set of receptors that are built specifically for sensing sweet tastes. As soon as your taste receptors get a whiff of sugar, they, like a cheetah chasing its prey, will send a sweetness signal to your brain at a high speed and with overwhelming strength. The sweet taste receptors on our taste buds pass messages along a chain of enzymes (your body’s worker bees), each one amplifying the signal along the way.

The enzymes in this pathway act like branches on a tree. One tree branch will split into two, which will split into more, and so on until they reach the sky. Taste reaches the brain in the same way. By the time the signal gets to the brain, it is being carried by an army of enzymes.  As a result, our brain knows right away what is going on and floods itself with feel-good chemicals that motivate you to eat more.

NOTE: Bitter taste is carried along a similar pathway. Your brain needs to know as soon as possible if you are eating something bitter, because bitterness is the taste that signals that something is toxic and needs to be purged and avoided in the future.

Not every carbohydrate-rich food is sweet, however. While some breakfast foods taste sweet because they’ve been doused with sugar (I’m looking at you Cinnamon Toast Crunch), most carbohydrate-rich foods, like pasta and bread, don’t taste sweet at all. Why is this?

Just like how a cable box is programmed to pick up particular tv channels, the taste receptors on your tongue are built to sense a particular type of sugar – monosaccharides, or single sugar molecules. In high-carb foods like bread and pasta, glucose is locked up in long, complex chains called starches, and our taste receptors cannot sense the presence of glucose in these chains.

Manufacturers of sugar substitutes like corn syrup artificially control the size of these starches to adjust the sweetness of their product. The shorter the starch, the sweeter the taste. In some cases, manufacturers use different sugar molecules, like fructose in their products. You’re probably itching to learn more about all of these modifications, and the role they play in manufacturing corn syrup. But that’s too much to explain in one blog post, so you’ll have to wait until the next one. Stay tuned!

Ben Marcus is a public relations specialist at CG Life. He received his Ph.D. in neuroscience from the University of Chicago. You can follow him on Twitter @bmarcus128.

On December 16, 2017 at about 5:00 PM CST, the asteroid 3200 Phaethon passed within 64 million miles of Earth. That’s about 27 times the distance to our Moon. While this may sound like a long distance (indeed, it would take on the order of one million hours to drive that distance in a car!), this particular approach will be our closest encounter with the asteroid for another 75 years.

With a diameter of 3.6 miles (about the distance from the Shedd Aquarium to the Lincoln Park Zoo in Chicago), 3200 Phaethon is the second largest asteroid we know of that could present a potential hazard to civilization. In fact, it is not much smaller than the 6 mile diameter asteroid that wiped out the dinosaurs 65 million years ago. 

Just last week, an enormous meteor exploded over Chicago with enough force to register a magnitude 2 earthquake. This, plus 3200 Phaethon’s proximity to Earth last month, are stark reminders that hazards within our neighborhood of the Solar System often come dangerously close to Earth.

Because of this threat, we cannot take our existence on this planet for granted. To preserve our safety, it is important to remain consistently vigilant of the threats posed by these asteroids, and to develop plans required to prevent the catastrophic extinctions that have taken place in the past. Thankfully, we have the means to detect and monitor dangerous asteroids in our vicinity, so there’s no need to start looking for the nearest bunker to retreat to for the apocalypse! With advanced warning and international cooperation, it is within our capabilities to save the Earth if it were to be in the path of an asteroid or any other large Near-Earth Object (NEO).

Near Earth Objects

An NEO is defined as any celestial object (namely asteroids or comets) with orbits that bring them within 1.3 times Earth’s distance from the Sun, or 1.3 astronomical units (AU). NEOs may be deemed potentially hazardous if they are larger than about 140 meters in diameter and if they are predicted to pass within 0.05 AU, or about 20 times the distance to the Moon, of Earth at closest approach. As of December 30, 2017, astronomers have detected 17,546 NEOs, of which 1876 are potentially hazardous. Astronomers detect these hazardous objects using ground-based telescopes as well as observational spacecraft such as the NEOWISE mission. NASA estimates that over 90% of the NEOs in space larger than 1 kilometer in diameter have been detected through programs like this to date.

The Chances of Getting Hit

Near Earth Objects come in all sizes. The probability of impact is inversely related to the size of the object, with small encounters being the most frequent and large catastrophic ones being few and far between. Using geologic evidence and even some historical accounts, we can understand the impact (no pun intended) of these collisions on the global ecosystem and past civilizations, as well as the risk we could expect from future threats.

The smallest NEOs (less than approximately 25 meters across) enter our planet’s atmosphere in tons every day, and they are too small and frequent to detect in advance. Thankfully, most burn up in our atmosphere well before they reach the planet’s surface, leaving no damage. When small objects burn up at night, we can see them as meteors, or shooting stars.  The largest meteors, known as fireballs, start as meteoroids the size of cars or larger, and are usually seen about once per year. In 2013, one of these fireballs went viral: the Chelyabinsk meteor that struck without warning in Russia. That meteoroid was about 15-20m in diameter (bigger than a school bus), and was the largest meteoroid to strike our planet  in over 100 years. The explosion sent a shockwave powerful enough to shatter windows and knock down structures in the vicinity, injuring approximately 1000 people.

Once every few thousand years, objects between 25m and 1km in size pass through the atmosphere to the surface as meteorites and are capable of causing great damage at a regional scale. Many can leave sizeable impact craters, such as Meteor Crater outside of Flagstaff, Arizona. Such collisions can leave geological evidence, allowing scientists to study the size and composition of the original object. The largest meteoroid to enter the atmosphere in recorded history was the 1908 Tunguska event in Siberia. Although the meteoroid in question disintegrated in the atmosphere without leaving a crater, the resulting explosion created a shock wave that was hundreds of times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki during World War II. As NASA explains, this was powerful enough to completely flatten forests over an 800 square-mile region and cause measurable changes in atmospheric conditions across the entire Eurasian continent!

Objects like 3200 Phaethon, which are larger than a kilometer or two, strike the Earth every few million years, and they produce catastrophic effects at a global scale. Perhaps the most well known is the impact behind the Cretaceous-Tertiary extinction that killed the dinosaurs, as well as the majority of other plant and animal species on the planet at the time. This event was widely discussed in the news in 2016, when drilling samples from the Chicxulub crater on Mexico’s Yucatán peninsula corroborated existing theories for the impact. While these large asteroids would be the most devastating, they are also the easiest to detect. NASA is vigilantly surveying and monitoring NEOs, enabling their detection so we could potentially deflect them before they cause a hazard to life as we know it.

Preventing Impact

A number of methods exist to divert the path of an approaching asteroid. For smaller hazards, this could be accomplished by striking the object directly with a high-speed rocket, or by sending a massive spacecraft to slowly tug the object off course using the force of its own gravity. To be effective, such methods require advance notice of a threat, especially for larger asteroids. While firing a projectile into an oncoming threat is the simplest to implement given our current technology, we are still decades away from seeing this as an option that is ready for immediate use. The gravitational tug method remains untested and may take even longer. The time it will take before these options become a reality highlights the importance of proactively monitoring NEOs.

For the largest of asteroids, or as a last resort after failed attempts on smaller options, NASA may have to resort to the nuclear option. This involves attacking the asteroid with a nuclear bomb to produce a massive explosion that deflects its path. This method risks fracturing the asteroid, sending potentially radioactive debris on a collision course with Earth. Nevertheless, this may be a highly effective technique if properly timed. The use of nuclear explosives in space violates the international Outer Space Treaty, however, which was signed in 1967. Bypassing such laws would require cooperation between many nations to avoid conflict.

While these particular options are all technologically feasible, governments have generally invested little in their implementation. As a result, even the most rudimentary of protective measures would require decades of development and preparation to ensure complete reliability when put to use. Because large impact events are sporadic, the proactive detection and monitoring of potentially hazardous objects in our planet’s vicinity is of critical importance for avoiding catastrophe; early warning gives our scientists and engineers the time needed to deflect an asteroid before it’s too late.

Flashes of fiery light.  Infinite sparkles.  The hardest rock on the scale.  A traditional symbol of both love and status.

Diamonds have fascinated people through the ages.  Their flashy optic properties captivate the viewer and make us wonder, “What is it about a diamond that makes the light bounce around and sparkle?”

In answer to that question, we have to explore the shape, purity, and physical properties of a diamond. Let’s start with shape.

Diamonds form from carbon that has been subjected to extreme pressure and heat underground for millions of years.  In their raw form, diamonds actually don’t sparkle at all.  To the untrained eye, they look like any old rock.  But when a trained gem cutter sees one, they begin to inspect it its weight, flaws, and optimal shape to find the best way to turn this raw rock into a collection of sparkling jewels.  A jeweler usually cuts this raw diamond to maximize its weight, while cutting out any large flaws or inclusions.  Large, chunky trimmings are subsequently cut into smaller diamonds.

It has been said that the round brilliant shape is the most sparkly of all the diamond cuts.  The round brilliant features 57 or 58 facets, or surfaces, which allow the light to enter the gemstone and bounce around, causing flashes of light.  (A diamond with a flat bottom, or culet, has 58 facets, and a diamond with a perfectly pointed culet will have 57.)  To achieve this shape with maximum sparkle, the diamond must be cut at precise angles so the light entering the stone bounces between the facets and is directed back up toward the viewer.   

Determining and using the optimal angles increases the aesthetic of a diamond so much that certain companies have even patented their cutting techniques.  Hearts on Fire advertises that they have an algorithm that cuts every diamond at the perfect angle, and Tiffany & Co. uses a proprietary combination of angles they say is unique to their jewelry.  But, what are these angles? That depends on a substance’s index of refraction, which is a measure of how much a substance bends light when it hits a surface boundary such as a facet.

 And if a diamonds have optimal angles, why don’t all jewelers use the same ones? 

Bending Light

Each substance has a different index of refraction, and therefore bends light at different angles.  By determining the index of refraction of a diamond, jewelers have been able to determine optimal angles for shaping diamonds so that they bend the maximum amount of light back to the viewer.   

 Gemstones with a higher index of refraction should be cut steeper to maximize their sparkle. A higher or lower refractive index doesn’t automatically make a stone sparkle more or less.  Rather, it dictates the precise angles at which the stone is cut to make light bounce in the right direction and make a stone sparkle.  A stone that is cut at angles that correspond with its refractive index will achieve its own maximum sparkle.  Diamond, and two well-known diamond simulants, moissanite and cubic zirconia, all have different indices of refraction;(3,4) therefore, the optimal angles for these three stones are all different, and each of these three stones should be cut differently to maximize their reflective properties.  Stones with a higher refractive index, such as moissanite, should be cut with steeper angles than stones with lower a refractive index, such as diamonds (2).

Cutting Diamonds to Maximize Sparkle

The Gemological Institute of America (GIA), an organization dedicated to researching and identifying gems and the developer of the Four C’s and diamond grading scales, says that each part of a diamond’s cut contributes to its overall appearance, but there are a few particular angles that are more important than others. Specifically, a precise crown angle, in combination with a mid-range pavilion angle, and a tiny culet are sure to produce some great sparkles.  

Crown Angle

The crown angle describes the angle between the flat, top surface and the crown, and the first edge that slopes downward, and is optimized between 32º and 36º (1).  This angle affects the diamond’s upward appearance, or the way it flashes light back up to the viewer.  While the flat octagonal table reflects white light back at the viewer, the crown facets act as prisms, and reflect rainbows of light in all directions (2).  If you’ve ever sat near a sunny window and twirled a diamond ring angled at a wall, you may have noticed an octagonal light reflected from the table, as well as many tiny rainbows, which are reflected from the crown facets. 

Pavilion Angle

Another angle that is critical for the diamond’s upward appearance is the pavilion angle, which describes the angle between the table and the bottom facets that meet at the culet.  If the pavilion angle is too shallow, incoming light will bend too much, and it will bounce off the first pavilion angle and then reflect out of the crown, without ever reaching the other side of the pavilion.  If the pavilion angle is too steep, the diamond will not bend the light sufficiently to reflect it back up at the viewer.  Instead, the light will leak out of the bottom and sides of the diamond.  However, at a mid-range pavilion angle (40.5º – 40.8º), light that enters the gemstone perpendicular to the table facet will bounce from one pavilion facet to the pavilion facet on the opposite side of the diamond, and then be reflected back up through the table, thus enhancing the diamond’s classical upward appearance. 

Culet

Finally, a third cut that makes a big difference in a diamond’s sparkle factor is the culet.  The culet measures how pointy the bottom of the diamond is.  A tiny culet helps the diamond sparkle more, and a large culet can negatively impact the diamond’s ability to reflect light upward.  That said, an extremely tiny, or pointed, culet can be sharp or fragile, and needs to be set carefully in jewelry.  For additional information on the other angles that contribute to the round brilliant cut, check out the GIA’s diamond guide (1, 5).

Get Involved

If you find yourself in the position to buy a diamond – or a moissanite or cubic zirconia – ask your jeweler about the angles of your stone.  Some diamonds are GIA certified, and come with special reports that include information on their angles, as well as other characteristics.  A reputable jeweler should know all about the physical properties of your diamond, and will likely be happy to tell you about it.  

Try it at Home

If you have a diamond, hold it under a magnifying glass and see if you can spot the sides of the octagonal table facet. How many facets can you count?  How pointy is the culet?  When you hold the stone up in sunlight near a window, can you see small rainbows reflecting out of the crown facets?

Sources

(1) https://www.gia.edu/diamond-cut/diamond-cut-anatomy-round-brilliant

(2) https://www.prosumerdiamonds.com/crown-angle/

(3) https://en.wikipedia.org/wiki/Cubic_zirconia

(4) http://www.moissanitevsdiamondrings.com/differences-between-moissanite-and-diamond/

(5) https://www.gia.edu/diamond-quality-factor

Dana Simmons is a Ph.D. Candidate in Neurobiology at The University of Chicago, and a lifelong gem enthusiast. Follow Dana on Twitter @dhsimmons1 and dana-simmons.com.

This story begins with a giant worm that lives in one of the most inhospitable places in the planet. A giant, gutless, eyeless worm.

In a historic exploratory voyage in 1977, Dr. Robert Ballard and his team found these majestic giant tube worms (Riftia pachyptila) towering over hydrothermal vents 8,000 feet deep in the sea along the Galápagos Rift . As they approached the seafloor, they noticed it was teeming with gushing black smoker chimneys. Below were 400℃ (752℉) acidic and sulfide-rich fluids spewing from the vents. Above was the relatively oxygen-rich, cooler, ambient seawater. The chemicals the vents release are toxic and released with high pressure, and that deep in the ocean, organic nutrients are scarce.

In these conditions, with extremely high temperatures, high acidity, low oxygen, and low nutrients, the researchers were not expecting to see a lush, diverse marine ecosystem. They were perplexed when they saw, not just living things, but a large community full of creatures of all sizes! Clams and mussels the size of dinner plates were scattered along the base of six-foot high tube worms, which were decorated with bright red plumes. Strange shrimp, squat lobsters, and crabs were seen crawling seamlessly along the seafloor, while eel-like zoarcid fish swam up above, looking for their next meal. How could such a rich community thrive in such a harsh environment?

They Key to Survival in the Deep Ocean

Microbiologist Colleen Cavanaugh had the same question as a first year graduate student at Harvard University in 1980. She was attending a lecture where the curator of worms at the Smithsonian Institution, Meredith L. Jones, was discussing giant tube worms and the mystery behind their survival. Jones had mentioned sulfur crystals found in the tube worm’s specialized organ called the trophosome. She and her colleagues thought this organ helps the worm survive by either breaking down toxins or providing nutrition for its sperm.

Incidentally, Cavanaugh had also recently attended a microbiology lecture, which got her thinking about microbes. From there, she proposed that the key to the trophosome’s function lied with some of its permanent residents: sulfur-eating bacteria. After obtaining a sample of trophosome tissue from Dr. Jones, Cavanaugh went on a quest to find these microscopic beings.

Using a high-powered microscope, Cavanaugh looked inside the trophosome and found small spheres 3-5 microns (thousandths of a millimeter) in diameter that were distinct from the rest of the tissue. She later confirmed that these spheres contained DNA, which meant that they could be bacteria.

Further examining the trophosome, Cavanaugh also found key enzymes involved in digesting sulfur and extracting the carbon from carbon dioxide. This finding further supporting her hypothesis that giant tube worms stay healthy by maintaining a symbiotic relationship with bacteria (meaning they’re two very different species who live in intimate association with one another). These tube worms have a special type of symbiosis with their bacteria called a mutualism, where both organisms benefit.

So, what’s the deal with these worms? Do they really have tiny organisms living in their tissues that help them survive? Humans and other terrestrial animals rely on gut and skin microbes to survive, so why not tube worms?

Giant Tube Worms and Bacteria Depend on Each Other

 Bacteria provide giant tube worms with food in exchange for shelter. The bacteria (the “symbiont”) use a process known as chemosynthesis to reap energy from hydrogen sulfide to make organic compounds that the giant worm (the “host”) can eat. Much like how plants and other organisms harness light as an energy source to make sugar through photosynthesis, these bacteria use the electrons from the hydrogen sulfide that spews from the vents (their “food”) and the oxygen from the ambient seawater to create the energy needed to convert CO₂ (inorganic carbon) into a form that the worms and other organisms can eat (organic carbon).

But the worms aren’t the only ones reaping the benefits from this partnership. The tube worms pull their weight by delivering the ingredients for its food directly to the bacteria. Specifically, they use a special type of hemoglobin to bind both oxygen and hydrogen sulfide at the same time and deliver them right to their symbiont. (Don’t try this at home: if you carried sulfur in your blood, you’d be in big trouble.)

The service these tube worms provide helps the bacteria solve a very tough conundrum they have to deal with by living around hydrothermal vents. To make organic carbon from CO₂, these bacteria need both oxygen and sulfur around. But as single-celled organisms, it can be very difficult for them to find these ingredients in the vast, open ocean. So, the tube worms find these compounds for them. These bacteria are like an adult who has cut a deal to move back in with their parents. They get to live in a cozy home (a trophos-home, if you will), and their hosts provide them with all of their groceries. But, to pay rent, these tenants have to cook their hosts’ meals with some of those groceries. Not so bad, ain’t it?

It’s all well and good until the host decides to eat some of the tenants. Indeed, giant tube worms have been found to occasionally digest their bacterial symbionts when they’re staving. But overall, it’s a great deal!

It’s an Open Relationship

 Two months after discovering the symbiotic relationship between tube worms and bacteria, Cavanaugh stumbled upon a scientific paper describing another unusual class of animal that lives on the ocean floor in seemingly inhospitable waters: gutless bivalves, like clams and oysters, that thrive in the sulfide-rich muds of eelgrass beds.

To her surprise, Cavanaugh did not find any sulfur crystals leading to the bivalve’s expected sulfur-eating bacterial symbionts. So, Cavanaugh tested for another enzyme that plants and other photosynthetic organisms use to convert carbon dioxide into usable carbon. This one is called RuBisCO. By tracing this enzyme in the bivalves, she identified trillions of chemosynthetic bacteria living in their gills that are almost identical to the ones found in the giant tube worms. Scientists hypothesize that this symbiotic relationship explains how they burrow into the ocean floor: they create Y-shaped tunnels, but they primarily live in the top half of the Y. Scientists think this allows them to have access to the oxygen-rich seawater above as well as the sulfide-rich sediments below. The nutrients are then able to flow over the gills to “feed” the bacteria while the bacteria “feed” the bivalve with organic molecules produced from sulfur. Does that sound familiar?

In all, Cavanaugh found two different marine invertebrates that live in two different sulfide-rich environments, yet have the same symbiotic association with the same chemosynthetic bacteria. She believed this meant that chemosynthetic symbioses are much more common than her predecessors thought. In fact, virtually all marine animals that live around hydrothermal vents survive because of the chemosynthetic bacteria that live in or on their cells.

In fact, within sulfide-rich sediments, scientists have found the same bacteria living in association with a variety of microscopic worms and other organisms. What’s more: scientists have also discovered methane-eating bacteria that serve as symbionts to some marine invertebrates around hydrothermal vents. These bacteria get their energy from methane instead of sulfur.

The Importance of Working Together

Much like plants and other photosynthetic organisms that are the base of food chains in terrestrial and some aquatic environments, chemosynthetic bacteria form the basis of food chains in environments where light is not available. Symbiotic relationships with chemosynthetic bacteria and larger marine animals allow both the host and symbiont to thrive in habitats and live in a way that would not otherwise be possible without their symbiotic partner. They are yet another example in nature that demonstrates the importance of working together.

For more information on chemosynthetic symbioses, take a look at Colleen Cavanaugh’s 20-minute talk for iBiology here. To learn more about the research Cavanaugh’s lab performs at Harvard University, venture over to the Cavanaugh lab website.

Emily Dodd is a graduate student at the University of Illinois, Chicago, where she is studying ecology and evolutionary biology.

Where would we be without blood? That red stuff that carries vital oxygen from our lungs to our muscles, and helps move our body’s chemical waste to where it can be recycled or disposed of? Blood is vital for life in humans, but did you know that not all animals have blood, and that some have blood that is very different to our own?

In fact, many small creatures, such as amoebas, sponges and corals, don’t need blood. Most of their body makes direct contact with the outside environment, which means they can survive by directly absorbing nutrients from their surroundings.  Furthermore, their waste can “leak” out by a process known as diffusion. For these animals, a heart, veins, arteries and blood would be an unnecessary investment.

The innards of larger animals, like humans, don’t have such a direct link to the outside world, so absorption and diffusion are not an option. Rather, they need a transport system in their bodies that can help stuff to get in, out and around. Specifically, our bodies need to move oxygen from our lungs to our cells to produce energy by burning the sugars, fats and proteins we eat in a controlled way. To solve the transport problem, many animals have developed some kind of circulatory system, made of an oxygen- and nutrient-carrying fluid, some plumbing, and sometimes one or more pumps to keep things moving.  In humans, the fluid is blood, and the plumbing is our veins, arteries and capillaries. The oxygen carrier in our blood is hemoglobin.

What is hemoglobin, and how does it work?

Hemoglobin is an incredible molecule, combining four long protein chains, four flat ring structures (known as heme) and four iron atoms, each held in the center of each heme ring.  Blood’s characteristic red color comes from the combination of iron and heme.  For hemoglobin to do its important work of transporting oxygen, it needs to not only pick up oxygen in the lungs, but also let go of it in the parts of the body where it is needed. It uses iron to bind the oxygen, and the rest of the hemoglobin molecule works as an efficient molecular machine to make sure the oxygen is bound loosely enough to be able to be dropped off at its destination.

The shape of the protein chains in hemoglobin control how much oxygen it binds or releases. When oxygen binds to the iron in one heme ring, it changes the shape of the four protein chains, making it easier for the other three heme groups to pick up oxygen atoms of their own (here’s a neat video that shows how this works). The protein chains are also sensitive to changes in pH and carbon dioxide concentrations, which allows oxygen to be released in actively metabolizing tissues, where the pH is low and the carbon dioxide concentration is high (like in active muscles).

Iron rusts by taking in oxygen, but hemoglobin is not like any iron nail.  If you want to get the oxygen (or iron) out of the rust, you need to do some pretty fancy chemistry. But the hemoglobin molecule, on the other hand, is nature’s way of holding the iron in a delicate balance, where it is able to bind oxygen loosely and reversibly, without “rusting” permanently.

Hemoglobin is packaged into red blood cells, which are specialised delivery cells that, unlike most other cells in your body, do not contain any DNA! Human red blood cells get rid of their nucleus (where the DNA is) as they mature, which gives them more space for hemoglobin, and makes them small enough to fit through the smallest blood vessels. Red blood cells are shaped like a donut without a hole. Their shape gives them a high surface area, allowing lots of space for oxygen to pass through. They are very flexible, and can squeeze through tiny blood vessels that are roughly half their diameter.

Pretty much all animals that have backbones (vertebrates) use hemoglobin to carry oxygen around. But what about invertebrates? Let’s take a look at some alternative solutions they’ve developed for the problem of carrying oxygen.  Spiders, crustaceans, octopuses, and squid, for instance, carry oxygen using a copper-based pigment known as hemocyanin, which makes their blood blue. This may seem weird, but it’s really not so surprising once you consider that creatures that look so different from us on the outside have different chemistry, too – hemoglobin is not the only answer! Unlike hemoglobin, hemocyanin is able to operate in low-oxygen environments and in the cold, making it perfect for deep sea creatures.

Some leeches and segmented worms use an iron-carrying pigment called chlorocrourin, which is particularly fun because it appears green when its diluted, and red when it is concentrated!

One more special case deserves a mention. There is, in fact, one creature that does have a backbone but doesn’t have hemoglobin. It’s the Antarctic icefish, which survives in icy cold water by simply dissolving oxygen in its blood without an oxygen carrier. This is only possible because cold water can carry a lot of dissolved oxygen, making it easier for the fish to capture it without an oxygen carrier like hemoglobin.

Our Blood Carries More Than Oxygen

Our blood carries lots of cells and molecules that perform functions, such as fighting infection, repairing blood vessels, and transporting chemical messages, such as hormones, around the body. Here are just a few of the different cells and molecules floating around in your blood right now:

• White blood cells. These cells, also known as leukocytes, work on many fronts to destroy and repel invaders, keeping our bodies clear of infection. Some white blood cells produce specialized molecules called antibodies that tag viruses and bacteria for destruction.
• Neutrophils. These are generally the first molecules to reach a site of infection. Along with macrophages (the “Pac-Men” of your blood) neutrophils engulf and digest bacteria, fungi and parasites. If you’ve ever looked at pus or seen that cloudy stuff that comes out of your nose when you’re sick, you’ve seen dead neutrophils: the aftermath of a bloody war against a foreign invader.
• Platelets and clotting factors. When the circulatory system springs a leak (such as when you cut yourself) your body needs to patch the hole to stop you losing too much blood. This repair job belongs to platelets, which gather at any sites of damage and start the process of forming a clot. The blood also contains clotting factors that continue the process and ultimately form a scab.

All these cells and molecules travel around in a straw-colored liquid called plasma. Plasma makes up more than half your blood volume, helping the cells and molecules get around, a bit like how water gets you moving on a water slide. Donated plasma is used to make treatments for a number for immune deficiencies (by replacing antibodies), bleeding disorders (by replacing clotting factors) and other conditions.

If you’d like to donate blood, check out one of the websites below to find a location in your part of the planet:

USA:

• https://www.redcrossblood.org/
• http://www.americasblood.org/about-us/our-member-blood-centers.aspx
• http://www.bloodsystems.org/

Canada: https://blood.ca/en

Australia:  http://www.donateblood.com.au/

UK: https://www.nhsbt.nhs.uk/donate/

New Zealand: https://www.nzblood.co.nz/

Alison Gould (BSc (Hons) PhD FRACI CChem) is a Scientific Communications Specialist in the Research and Development Team at the Australian Red Cross Blood Service. You can follow her on Twitter @A2ali.

My first memory of knitting wasn’t of my grandmother making a scarf by a roaring fire, though it did involve a stern matron overlooking my work as her needles clacked together, knitting a blanket as we took out our pencils and our Scantrons.

One of my high school math teachers, Mrs. Danielvich, loved knitting, and one reason for this was the complex problem solving behind it. No yarn was the same, no set of needles was perfect for all projects, and to complete a pattern, she often needed to perform various calculations to map out the different blankets and sweaters she worked on during our finals.

Or so she explained to us before our test began.

At the time, I rolled my eyes and dipped further into my Algebra II problems, disinterested in her chosen hobby, which I chalked up to her distinguished age and her profession as a math teacher. But a few months later, when I started my freshman year at University of Oregon, I found myself surrounded by students who purled and spun while studying for their Biology 202 exams. I was finally drawn into the craft, and I soon found myself knitting hats between class and my lab work at the Coastal Archaeology Lab.

It’s not a secret that knitting lends itself to be a great hobby for any scientist. It allows creativity to shine (Riley et al, 2013), especially for those who are really into letting their geek flags fly. It’s a cheap hobby, (one can find needles and yarn for $5 or less at Goodwill, perfect for the poor graduate student or busy individual. It’s a portable hobby, easily stuffed into a backpack (or, perhaps, a lab coat, though I wouldn’t recommend it).

But, in addition to the ease in which knitting can fit in the average life of the working research professional, knitting also carries some real health benefits.

Knitting is Good for Your Health

The physiological effects of knitting can be surprising to those who have never taken up the art form before (arts and crafts are defined liberally here, folks). Studies have been shown that knitting can lower a person’s blood pressure, and in individuals with eating disorders, knitting has been shown to reduce stress levels (Clave-Brule et al, 2009). Knitters have been found to pick at their fingers and bite their nails less while they’re partaking in this craft, not only because their hands are busy, but also because of its aforementioned calming effect (Greer, 2008).

Forget the health benefits, you say. By now you’re probably wondering why such a bizarre hobby works. Because let’s face it–it’s twisting string together with two small rods–how could that possibly translate into anything useful?

Let’s start with the basics–first, you need wool. Today, yarn comes from all sorts of sources, ranging from the cheapest, factory made acrylic to the softest, most delicate musk oxen hair. But originally, we collected wool from the sheep and goats found throughout the Mediterranean, where, coincidentally, the first archaeological artifacts of knitting were located. The 11th century Coptic Egyptians’ craft? The sock! (Burnham, 1970).

No sheep is the same (with the exception of the clone Dolly, of course). In fact, like dogs, sheep come in several different breeds. The breed not only tells ranchers (and scientists, and knitters for the matter) what to expect from their offspring, but how much wool and the type of wool they will produce. With that being stated, wool and other animal fibers react the same way when faced with elements, as we will discuss below.

The Thick and the Thin of Yarn

First and foremost, not all yarn that you may see at your local knitting store is made from the same source – some are made from wool, and others are made from acrylic or cotton. Wool–mostly from sheep– feels different then other fibers like cotton because of its chemical composition. Wool, which comes from animals, of course, and it is mostly comprised of proteins and fat molecules. Meanwhile, cotton comes from a plant, and it is composed of cellulose, a complex sugar chain. The chemical compounds of the two are why knit cotton socks may feel more light, but wool socks may feel a lot more warm and stretchy. Wool’s chemical structure makes it more elastic, as well as helps it take in more water and make it more resistant to fire than most fibers (D’Arcy, 1986).

Icelandic sheep and other breeds from the North Atlantic grow thick, almost scratchy wool. This tough fiber make for coarse yarn that binds together when hit with rain and snow, making it ideal for protection. Should you observe this wool under a microscope, you will find the fibers fraying and clotting together when faced with especially wet and cold weather. Believe it or not, the borderline uncomfortable Irish sweater you may have worn during a South Side Irish parade is practical, because it traps in the heat of the wearer’s body while repelling precipitation, be it late March sleet or a badly poured Guinness from Cork and Kerry’s Pub.  

Of course, you’ll probably notice this when move from the sleet of Western Ave to the warmth of Mrs. Ryan’s parade party. When you enter the warm house, the trapped water in your sweater will steam itself out of the wool, into the air–carrying over an evolutionary tactic that developed in ungulates’ wool to prevent the animal from losing body heat in colder climates.

Twist and Pull, Two and Fro

So, we’ve got a basic idea of what wool can do, as well as why knitting is physiologically up there as good as giving up smoking and taking up yoga.

Why knit?

You could help calm your busy mind, or you could engage in your own science experiment. Go out to your nearest store (or order from Amazon, I don’t judge), find a Youtube how-to channel, and test out the different feels between cotton and wool.

Then start adding up the different weights of them.

It would make my math teacher proud.

Sources:

D’Arcy, J. B., Sheep and Wool Technology, NSW University Press, Kensington, 1986 ISBN 0-86840-106-4

Dorothy K. Burnham. “Coptic Knitting: An Ancient Technique”. Pasold Research Fund, 1970.

Clave-Brule, M., Mazloum, A., Park, R. J., Harbottle, E. J., & Birmingham, C. L. (2009). Managing anxiety in eating disorders with knitting. Eating and Weight Disorders-Studies on Anorexia, Bulimia and Obesity, 14(1), e1-e5.

Riley, J., Corkhill, B., & Morris, C. (2013). The benefits of knitting for personal and social wellbeing in adulthood: Findings from an international survey. British Journal of Occupational Therapy, 76(2), 50-57.

Leapman, Melissa (2006). Cables Untangled: An Exploration of Cable Knitting, PotterCraft.

Cancer is such a scary word. It comes in many different types, and chances are, it has touched your life in some way, whether through you or a loved one. The lifetime odds that you’ll end up with cancer are about four in ten, and the odds that it takes your life are about one in five. It feels like cancer is everywhere these days, not only in personal stories, but in the fundraisers, celebrity spokespeople, and political speeches on our televisions. In a general sense, this disease can seem daunting to tackle. But on a personal level, one thing is sure – we’ve all seen the toll cancer has on our families and loved ones, and we all aim to prevent it in our own lives.

But figuring out how to keep cancer at bay can seem like a confusing mess. There is a lot of misinformation and partial truths out there. So how do we know who to listen to? How do we evaluate research meaningfully when it’s presented to us in a short news clip on Facebook? How can we suss out people trying to deliberately mislead us from those who are simply uninformed? It can seem frustrating, for instance, when one day, you read that fiber will prevent cancer and the next day you see another study claiming it’ll increase your risk.

So let’s talk about what cancer is and isn’t, what’s holding researchers back from finding a cure , and what you can realistically do to prevent cancer.

What Is Cancer?

First of all, cancer is not a single disease. There is a type of cancer for just about every organ in your body (think heart, lung, colon, brain…) and of those, cancer comes in many subtypes for the different types of cells that make up an organ.

A good example is blood cancer, or leukemia. You have different types of healthy blood cells in your body – the most commonly known are red blood cells (which feed your body with oxygen) and white blood cells (a group of cell types that fight infection). Each of these cells types can become cancerous.

Cancer is simply what happens when a healthy cell’s functions go haywire – and this can happen in multiple ways. Healthy cells do all the same things cancer cells do, but in a carefully controlled and regulated manner. Usually, cancer results from different genetic mutations that lead the cell to change its behavior in a harmful way: It consumes too much food, it replicates too fast, it changes shape, it doesn’t die when it’s supposed to, or it moves to different parts of the body. A single cancer-causing mutation is often not a problem; that mutation can be stifled by protective processes your body activates when things go wrong. But combine several mutations and let them fester, or damage the genes that protect you, and those cancerous cells can grow and proliferate uncontrollably.

Why Is Finding a Cure So Difficult?

Researchers spend time investigating how mutations arise. People can be born with cancerous mutations, or they can develop during someone’s lifetime from environmental causes such as smoking or sun exposure. However, a cancer researcher’s job is largely to figure out the molecular differences between healthy and cancerous cells, and to find a way to either a) stop cancers from spreading or b) prevent them from causing more harm. There are tens of thousands of researchers out there receiving millions of dollars to study cancer, and it often feels like we’ve barely made progress since the United States Congress started funding the “War on Cancer” in 1971.

Often, labs will study a single gene and its role in a single type of cancer – it can take years to determine exactly how a mutated gene causes cancer and how to go about fixing it. Meanwhile, another lab may find the same gene behaves differently in another type of cancer. This means that even within the research community, it can be difficult to achieve a consensus on what drives cancer. It also means that since so many different factors contribute to cancer growth, and since each person has different genes and is exposed to different environments, there is no single cure for cancer.

Despite this challenge, we have made progress with various cancer types. In fact, we understand much more about how a lot of cancers work. Scientists have developed chemotherapies that target specific cancers in specific patients based on their DNA.  Palliative care has also improved.

Even a modest extension of life can feel like a victory to those who have loved ones with cancer. “Okay fine,” you say, “But I read about amazing new discoveries about cancer in the news every day! Where are those cures I keep hearing about?!” This is fair to ask, but the true answer to that question is complicated. Research progress is slow, and change is often incremental. This is incredibly frustrating when we simply want answers, but it is also the reality of things. Since each cancer is really unique to its host, there is no one-stop-shop for a cure.

If I Can’t Trust Mainstream News, Then How Do I Really Reduce My Risk For Cancer?

The best thing you can do to prevent cancer is to stop reading about “miracle cures” and simply try to live a generally healthy lifestyle. Eat your veggies and skip the extra scoop of ice cream. Try to get up and away from your desk from time to time, build meaningful relationships with the people around you, and don’t stay up all night on the internet. The precise number and type of apples you eat per day aren’t going to keep the oncologist away, but having the fruit instead of a slice of pie just might.

Note: for a wonderful breakdown of cancer research and its impact on scientific progress, public policy, and personal lives, I heartily recommend Siddhartha Mukherjee’s The Emperor of All Maladies: A Biography of Cancer.

Stefanie Kall is a Ph.D. candidate in biochemistry at the University of Illinois, Chicago.

A mystery red gemstone is in front of you on a table.  Is it a ruby?  Is it a garnet?  Is it a red diamond? 

The DeYoung Red Diamond, held in the Smithsonian’s National Gem Collection in Washington D.C., presents a perplexing case.  Observers originally thought the deep red 5.03-carat gem was a garnet. The large stone was set in a pin and purchased by a Boston jeweler at a flea market.  The jeweler, S. Sydney DeYoung, noticed that stone held up better over time than a garnet should. After some testing, he realized that his stone was actually a rare red diamond. He extracted it from the pin and willed it to the Smithsonian, where it is now on display.

DeYoung’s story shows how easily a diamond can be mistaken for another gemstone if it isn’t colorless.  Traditionally, we think of diamonds as colorless, crystal clear, sparkly gemstones.  But most of them aren’t. In fact, the Gemological Institute of America (GIA) classifies diamond colors on a scale from D to Z.  Diamonds from D to F are considered colorless, and diamonds at the end of the alphabet have a yellowish hue.  The GIA has master color diamonds for each letter and classifies new stones against these standards.

Beyond these faint, yellowish color differences, some diamonds reflect colors across the spectrum.  These “fancy diamonds” come not only in yellow, but also brown, red, pink, and plenty of other colors, and they’re quite rare.  A colorless diamond is made up entirely of carbon atoms that have come together over millions of years under intense heat and pressure, while fancy colored diamonds take up impurities – non-carbon atoms – during formation.  Diamonds form in the presence of other elements, which get incorporated into the diamond’s carbon lattice structure and reflect colors other than white.  For example, diamonds with boron atoms woven into their molecular structure have a blue hue.  The more boron, the darker the blue. Diamonds with nitrogen impurities appear yellow, and diamonds with defects in their lattice structure appear brown.  Occasionally, diamonds form near sources of radiation, which is thought to perturb their structure and give them a greenish hue.  The causes of pink and red infiltration into a diamond’s structure remain elusive.

 The GIA grades the color saturation of fancy diamonds not with letters but with a more subjective scale: “light, normal, intense, or vivid”.  While color reduces the value of diamonds on the D to Z scale, fancy colors are valued more subjectively. When selecting colored diamonds, it’s more important to select a hue that you personally find beautiful than to worry about whether the stone is pure.

In addition to the “D to Z” diamonds and the “fancy colored” diamonds, there is a third color scale for brown diamonds.  Brown diamonds are considered fancy if their color is much more saturated than a diamond that registers as Z on the traditional D to Z color scale.  Unlike other colored diamonds which contain impurities, the brown color is thought to come from defects in the molecular lattice structure.  Until a few decades ago, these diamonds weren’t used in jewelry – they were only used in factories. But recently, Le Vian Jewelers rebranded brown diamonds as “chocolate diamonds,” which have bright brown tones.  

Although it could be easy to mistake a red diamond, such as the DeYoung Red Diamond, for a garnet or ruby by eye, the true difference is easy to spot when you zoom all the way in on the stone’s molecular structure. As you now know, a diamond is composed entirely of carbon atoms arranged in a strong tetrahedral structure.  Garnets are a totally different story because they involve several different atoms.  The general chemical formula for a garnet is X₃Y₂(SiO₄)₃, where the X position is filled by ions missing two electrons (divalent cations) such as calcium, manganese, iron, or magnesium.  The Y position is filled by ions missing three electrons (trivalent cations) such as aluminum, iron, or chromium.  The different combinations of these cations lead to different colors of garnets.  The ions in the X and Y positions form an octahedral shape, and the [SiO₄]4- ions form a tetrahedral shape.  All together, garnets have a combined octahedral/tetrahedral shape.  Fun fact: A 2008 study in the Journal of Gemology found that garnets also show some magnetic properties, which helps to identify them.

Rubies, like sapphires, are a type of hexagonal corundum.  In fact, rubies and sapphires are really the same gem.  The difference is only the amount of chromium impurities that seep into the chemical structure.  The chemical formula for a ruby is Al₂O₃.  If the entire ruby is formed from aluminum and oxygen ions, then the stone will be colorless.  However, color appears when the position of the aluminum ions is usurped by chromium ions.  If less than 1% of the aluminum is replaced chromium, then the stone will be red and called a ruby.  The difference between rubies and sapphires kicks in at the 1% chromium threshold.  Pink sapphires have slightly more than 1% of chromium, and it can often to be difficult to distinguish them from rubies.  If chromium takes over more than 1% of the aluminum spots, then the gem is a sapphire, and it can be blue or many other colors – depending again on the percentage of chromium.  Perhaps we should start referring to white sapphires as white rubies!

Getting down to the atomic level of gems to determine their molecular structure helps us learn about their properties, but requires quite a bit of laboratory equipment.  One method for determining the molecular structure of a gemstone is called X-ray crystallography.  In this technique, researchers send a beam of x-rays through a crystal.  The path of the beam is bent when it passes through the crystal, and this results in a unique dot pattern.  Each type of crystal gives its own unique dot pattern.  Think of the dot pattern as if it were the crystal’s fingerprint.  Once you obtain a dot pattern, your next step is to figure how the phase of each x-ray changed when it hit the spot where the dot is.  The change in phase will tell you if the x-ray has hit an electron along the way or not.  X-ray crystallography tells you where all the electrons are in the crystal. Once you know the number of electrons that are clustered together, you can figure out which elements are in the crystal, and you can determine how they are bonded together. (Fun fact: X-ray crystallography was used to determine the molecular structure of DNA around 1951-1953 by Rosalind Franklin, James Watson, and Francis Crick.)

While diamonds come in many deceiving colors, many other gemstones that we typically associate with colors also come in white/colorless varieties and look much like diamonds. Sapphires, for example, most often come in blue, but they’re also found as colorless stones.  Without careful examination, one could easily mistake a white sapphire for a diamond.  The untrained eye is unlikely to notice that a white sapphire is cloudier than a diamond and doesn’t split light into rainbows like a prism, as a diamond does.  Other stones, like topaz, moissanite, and zircon look so much like diamonds, that they’re often billed as diamond-simulants.  These stones are natural like diamonds, but they differ in certain properties, like reflectivity and hardness. They are more affordable than diamonds, however, and can be used as a substitute in jewelry.  

Moissanite is a naturally occurring gemstone whose formula is SiC.  Henri Moissan was the first person to find moissanite crystals in a crater left by a meteor in Arizona.  He initially thought they were diamonds, but later identified them as silicon carbide instead of pure carbon.  Moissanite is quite rare and is usually found as an inclusion inside another stone, or as a piece left behind from a meteor.  Silicon carbide (moissanite) forms in a complex hexagonal/dihexagonal structure, pictured on the right.

To the non-expert, diamonds and other stones can look so similar that people might not know if the two photos below were switched!  Are they diamonds, cubic zirconia, or topaz? Answer: They’re not switched because the ISC’s scientists feel compelled to cite sources correctly.)  The true difference in these stones becomes apparent when we zoom into the molecular structure.  Upon close examination, we can learn that different gems have different molecular structures, atomic compositions, densities, hardnesses, and refractive indices.  Regardless of which type of gem may interest you, make sure you consult with a reputable expert so you know what you are buying.

Get involved:

Visit the Grainger Hall of Gems in the Field Museum of Natural History in Chicago.  Take a look at their collection of diamonds and other colorless gems.  Can you spot differences in the way they reflect light?  Are they cut differently?  How do you think the fancy colored diamonds reflect light differently than the colorful ones?

Written by Dana Simmons, a Ph.D. Candidate in Neurobiology at The University of Chicago, and a gem enthusiast.  Follow Dana @dhsimmons1 and dana-simmons.com.