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Deep beneath the geysers and hot springs 
of Yellowstone Caldera

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lies a magma chamber produced by a 
hot spot in the earth’s mantle.

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As the magma moves towards 
the earth’s surface,

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it crystallizes to form young, 
hot igneous rocks.

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The heat from these rocks drives 
groundwater towards the surface.

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As the water cools, ions precipitate out 
as mineral crystals,

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including quartz crystals from silicon 
and oxygen,

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feldspar from potassium, aluminum, 
silicon, and oxygen,

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galena from lead and sulfur.

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Many of these crystals have signature 
shapes—

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take this cascade of pointed quartz, 
or this pile of galena cubes.

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But what causes them to grow into these
shapes again and again?

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Part of the answer lies in their atoms.

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Every crystal’s atoms are arranged 
in a highly organized, repeating pattern.

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This pattern is the defining 
feature of a crystal,

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and isn’t restricted to minerals—

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sand, ice, sugar, chocolate, ceramics, 
metals, DNA,

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and even some liquids have 
crystalline structures.

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Each crystalline material’s atomic 
arrangement

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falls into one of six different families:

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cubic, tetragonal, orthorhombic, 
monoclinic, triclinic, and hexagonal.

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Given the appropriate conditions,

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crystals will grow into geometric shapes

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that reflect the arrangement 
of their atoms.

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Take galena, which has a cubic structure 
composed of lead and sulfur atoms.

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The relatively large lead atoms

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are arranged in a three-dimensional 
grid 90 degrees from one another,

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while the relatively small sulfur atoms 
fit neatly between them.

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As the crystal grows, locations like these
attract sulfur atoms,

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while lead will tend to 
bond to these places.

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Eventually, they will complete the grid 
of bonded atoms.

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This means the 90 degree grid pattern 
of galena’s crystalline structure

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is reflected in the visible 
shape of the crystal.

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Quartz, meanwhile, has a hexagonal 
crystalline structure.

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This means that on one plane its atoms 
are arranged in hexagons.

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In three dimensions, these hexagons are 
composed of many interlocking pyramids

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made up of one silicon atom 
and four oxygen atoms.

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So the signature shape of a quartz 
crystal

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is a six-sided column with pointed tips.

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Depending on environmental conditions,

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most crystals have the potential to form
multiple geometric shapes.

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For example, diamonds, which form deep
in the earth’s mantle,

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have a cubic crystalline structure and can
grow into either cubes or octahedrons.

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Which shape a particular 
diamond grows into

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depends on the conditions where it grows,

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including pressure, temperature, 
and chemical environment.

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While we can’t directly observe growth 
conditions in the mantle,

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laboratory experiments have shown some
evidence

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that diamonds tend to grow into cubes at 
lower temperatures

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and octahedrons at higher temperatures.

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Trace amounts of water, silicon, 
germanium, or magnesium

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might also influence a diamond’s shape.

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And diamonds never naturally grow into the
shapes found in jewelry—

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those diamonds have been cut to 
showcase sparkle and clarity.

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Environmental conditions can also 
influence whether crystals form at all.

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Glass is made of melted quartz sand,

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but it isn’t crystalline.

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That’s because glass cools 
relatively quickly,

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and the atoms do not have time to arrange
themselves

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into the ordered structure 
of a quartz crystal.

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Instead, the random arrangement 
of the atoms in the melted glass

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is locked in upon cooling.

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Many crystals don’t form geometric shapes

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because they grow in extremely close 
quarters with other crystals.

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Rocks like granite are full of crystals,

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but none have recognizable shapes.

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As magma cools and solidifies,

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many minerals within it crystallize at the
same time and quickly run out of space.

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And certain crystals, like turquoise,

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don’t grow into any discernible geometric
shape in most environmental conditions,

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even given adequate space.

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Every crystal’s atomic structure has 
unique properties,

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and while these properties may not have
any bearing on human emotional needs,

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they do have powerful applications 
in materials science and medicine.