Deep beneath the geysers and hot springs 
of Yellowstone Caldera

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

As the magma moves towards 
the earth’s surface,

it crystallizes to form young, 
hot igneous rocks.

The heat from these rocks drives 
groundwater towards the surface.

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

including quartz crystals from silicon 
and oxygen,

feldspar from potassium, aluminum, 
silicon, and oxygen,

galena from lead and sulfur.

Many of these crystals have signature 
shapes—

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

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

Part of the answer lies in their atoms.

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

This pattern is the defining 
feature of a crystal,

and isn’t restricted to minerals—

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

and even some liquids have 
crystalline structures.

Each crystalline material’s atomic 
arrangement

falls into one of six different families:

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

Given the appropriate conditions,

crystals will grow into geometric shapes

that reflect the arrangement 
of their atoms.

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

The relatively large lead atoms

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

while the relatively small sulfur atoms 
fit neatly between them.

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

while lead will tend to 
bond to these places.

Eventually, they will complete the grid 
of bonded atoms.

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

is reflected in the visible 
shape of the crystal.

Quartz, meanwhile, has a hexagonal 
crystalline structure.

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

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

made up of one silicon atom 
and four oxygen atoms.

So the signature shape of a quartz 
crystal

is a six-sided column with pointed tips.

Depending on environmental conditions,

most crystals have the potential to form
multiple geometric shapes.

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

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

Which shape a particular 
diamond grows into

depends on the conditions where it grows,

including pressure, temperature, 
and chemical environment.

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

laboratory experiments have shown some
evidence

that diamonds tend to grow into cubes at 
lower temperatures

and octahedrons at higher temperatures.

Trace amounts of water, silicon, 
germanium, or magnesium

might also influence a diamond’s shape.

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

those diamonds have been cut to 
showcase sparkle and clarity.

Environmental conditions can also 
influence whether crystals form at all.

Glass is made of melted quartz sand,

but it isn’t crystalline.

That’s because glass cools 
relatively quickly,

and the atoms do not have time to arrange
themselves

into the ordered structure 
of a quartz crystal.

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

is locked in upon cooling.

Many crystals don’t form geometric shapes

because they grow in extremely close 
quarters with other crystals.

Rocks like granite are full of crystals,

but none have recognizable shapes.

As magma cools and solidifies,

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

And certain crystals, like turquoise,

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

even given adequate space.

Every crystal’s atomic structure has 
unique properties,

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

they do have powerful applications 
in materials science and medicine.