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Deep beneath the geysers and hot springs [br]of Yellowstone Caldera

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

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As the magma moves towards [br]the earth’s surface,

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it crystallizes to form young, [br]hot igneous rocks.

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The heat from these rocks drives [br]groundwater towards the surface.

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As the water cools, ions precipitate out [br]as mineral crystals,

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including quartz crystals from silicon [br]and oxygen,

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feldspar from potassium, aluminum, [br]silicon, and oxygen,

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galena from lead and sulfur.

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Many of these crystals have signature [br]shapes—

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

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But what causes them to grow into these[br]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 [br]in a highly organized, repeating pattern.

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This pattern is the defining [br]feature of a crystal,

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and isn’t restricted to minerals—

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sand, ice, sugar, chocolate, ceramics, [br]metals, DNA,

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and even some liquids have [br]crystalline structures.

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Each crystalline material’s atomic [br]arrangement

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falls into one of six different families:

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cubic, tetragonal, orthorhombic, [br]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 [br]of their atoms.

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Take galena, which has a cubic structure [br]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 [br]grid 90 degrees from one another,

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while the relatively small sulfur atoms [br]fit neatly between them.

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As the crystal grows, locations like these[br]attract sulfur atoms,

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while lead will tend to [br]bond to these places.

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Eventually, they will complete the grid [br]of bonded atoms.

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

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is reflected in the visible [br]shape of the crystal.

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Quartz, meanwhile, has a hexagonal [br]crystalline structure.

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

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

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made up of one silicon atom [br]and four oxygen atoms.

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So the signature shape of a quartz [br]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[br]multiple geometric shapes.

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

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

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Which shape a particular [br]diamond grows into

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depends on the conditions where it grows,

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including pressure, temperature, [br]and chemical environment.

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

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laboratory experiments have shown some[br]evidence

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that diamonds tend to grow into cubes at [br]lower temperatures

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and octahedrons at higher temperatures.

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Trace amounts of water, silicon, [br]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[br]shapes found in jewelry—

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those diamonds have been cut to [br]showcase sparkle and clarity.

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Environmental conditions can also [br]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 [br]relatively quickly,

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and the atoms do not have time to arrange[br]themselves

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into the ordered structure [br]of a quartz crystal.

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Instead, the random arrangement [br]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 [br]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[br]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[br]shape in most environmental conditions,

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even given adequate space.

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Every crystal’s atomic structure has [br]unique properties,

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

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they do have powerful applications [br]in materials science and medicine.