Why Did the Crystal Cross the Road? | Natural History Museum of Los Angeles

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Why Did the Crystal Cross the Road?

How crystals inspire research at neighboring institutions, NHMLA and USC

A quartz specimen from the Gem and Mineral Collections.

 

Everyone’s heard of crystals, but what exactly are they? So glad you asked. Here we go: it’s a solid with a highly ordered microscopic structure. That means when you get down to the very tiny scale of atoms and molecules (which are groups of atoms), there is a very regular pattern repeating over and over again. It’s called a crystal lattice. This microscopic order often leads to a stunning pattern at the much larger scale we can see with the naked eye.

a photo of a green crystal with small sections of white
This crystal is a mix of emerald and apatite: the green part is emerald, and the white is apatite. They both form hexagonal-shaped crystals because the atoms are arranged in hexagons. Photo by Robert Weldon, GIA.

And crystals aren’t just the shiny, translucent ones like quartz, rubies, and diamonds. Gold is a crystal as well, as is the graphite in your pencil. Sugar and salt can form crystals, too. Even oh-so-familiar ice is a crystal, made of water molecules (which becomes a bit more believable when you look at closeup photography of snowflakes).

a closeup photo of a snowflake showing its complexity
Macro photography of snowflakes shows their amazing complexity. Photo by Alexey Kljatov.

It might sound now like any uniform-looking solid is a crystal, but glass, for instance, is not because at the molecular level, it’s a jumbled mixture, not a perfect repeating pattern.

So how do these highly organized repeating patterns emerge in crystals? In the Mineral Science Lab at NHMLA, Associate Curator Aaron Celestian is researching how crystals grow. It might come as a shock to some, but we don’t fully understand how crystals naturally form; no theory quite explains the physical process that leads to such orderly arrangements happening all by themselves. People are looking into it, but the experiments to observe crystallization are extremely challenging because bonds form and break so fast it’s hard to keep track of it all. 

Undeterred, Celestian is measuring the crystallization process for epsomite, the crystal in Epsom salts (named after a deposit in Epsom, a small town in England). This crystal — often colorless or white with tints of yellow, green, and pink — forms on limestone cave walls and sometimes at the mouths of volcanoes. 

Celestian will be monitoring the structure of epsomite before and after crystals form using a specialized Raman microscope. His work will help us better understand how crystals take shape at the atomic scale, and it will also tell us more about the conditions required for them to form, which has all sorts of interesting applications. If we know what allows them to grow, the presence of certain crystals in layers of sediment can tell us about climate conditions in Earth’s past or even on other planets. Woah.

a photo of Aaron Celestian in his lab in the Mineral Science Department.
Associate Curator Aaron Celestian uses a compound light zoom microscope in the Mineral Science Lab.

Just across the street (Exposition Blvd, to be exact) the USC Chemistry Department also works with crystals. They’re used in a variety of research, from designing better solar cells to using lasers to “see” chemical reactions.

Professor Richard Brutchey finds new ways to make nanocrystals — as in, really, really small crystals. Depending on their size and shape, they have certain properties, so you can design and build crystals that are ideal for things like solar cells or LEDs (light-emitting diodes), which can be used in incredibly efficient light bulbs. 

“Many of the materials we use are based on mineral types found in the Museum, like pyrite and chalcopyrite,” said Brutchey. 

In addition to being the subject of research, crystals can also be important tools: they’re actually a key component in lasers. Crystals bend and split light, which allows researchers to select a very specific wavelength of light for a laser beam. And what can you do with a laser beam in a chemistry lab? You can excite chemicals, and you can observe them.

Professor Hanna Reisler uses lasers to jumpstart chemical reactions, finding the exact wavelength of light that breaks chemical bonds. This helps us better understand the fundamentals of how chemical reactions work — how bonds between atoms break and form. 

“Lasers allow us to place a specific amount of energy in a specific portion of a molecule or compound, helping us to focus on one tiny piece of the puzzle at a time,” said Jessie Parr, USC Associate Professor of Chemistry and former graduate student in Professor Reisler’s research group.

Professor Andrey Vilesov uses lasers to observe chemicals by suspending them in supercooled helium droplets. Why supercooled, and why helium? At extremely, extremely low temperatures (hence the “supercooled” part), helium is a very stable, unreactive liquid. It’s an ideal background to observe molecules because they don’t interact with the helium at all. By shining a laser at chemicals in supercooled helium, you can “see” their structure, which can help us better understand how chemicals function on this very small scale. 

So why did the crystal cross the road? To get to the chemistry on the other side!

 

Author’s note: This article was a collaboration between USC Professor Jessie Parr and NHMLA writer Katie McKissick.  

 

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