0:00:06.886,0:00:11.216
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,

0:00:32.882,0:00:36.876
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—

0:00:47.736,0:00:52.856
take this cascade of pointed quartz, [br]or this pile of galena cubes.

0:00:52.856,0:00:57.321
But what causes them to grow into these[br]shapes again and again?

0:00:57.321,0:01:00.013
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.

0:01:04.933,0:01:08.508
This pattern is the defining [br]feature of a crystal,

0:01:08.508,0:01:10.518
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

0:01:22.459,0:01:25.699
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,

0:01:34.359,0:01:37.009
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.

0:02:17.973,0:02:22.103
This means that on one plane its atoms [br]are arranged in hexagons.

0:02:22.103,0:02:27.564
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.

0:02:56.261,0:02:58.861
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,

0:03:09.128,0:03:11.868
laboratory experiments have shown some[br]evidence

0:03:11.868,0:03:15.838
that diamonds tend to grow into cubes at [br]lower temperatures

0:03:15.838,0:03:19.026
and octahedrons at higher temperatures.

0:03:19.026,0:03:23.496
Trace amounts of water, silicon, [br]germanium, or magnesium

0:03:23.496,0:03:26.646
might also influence a diamond’s shape.

0:03:26.646,0:03:31.256
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.

0:03:36.474,0:03:41.621
Environmental conditions can also [br]influence whether crystals form at all.

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Glass is made of melted quartz sand,

0:03:44.126,0:03:45.686
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

0:03:51.646,0:03:54.576
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

0:03:58.346,0:04:00.906
is locked in upon cooling.

0:04:00.906,0:04:03.546
Many crystals don’t form geometric shapes

0:04:03.546,0:04:08.146
because they grow in extremely close [br]quarters with other crystals.

0:04:08.146,0:04:10.809
Rocks like granite are full of crystals,

0:04:10.809,0:04:13.379
but none have recognizable shapes.

0:04:13.379,0:04:15.539
As magma cools and solidifies,

0:04:15.539,0:04:21.249
many minerals within it crystallize at the[br]same time and quickly run out of space.

0:04:21.249,0:04:23.881
And certain crystals, like turquoise,

0:04:23.881,0:04:28.891
don’t grow into any discernible geometric[br]shape in most environmental conditions,

0:04:28.891,0:04:31.014
even given adequate space.

0:04:31.014,0:04:34.204
Every crystal’s atomic structure has [br]unique properties,

0:04:34.204,0:04:39.134
and while these properties may not have[br]any bearing on human emotional needs,

0:04:39.134,0:04:44.204
they do have powerful applications [br]in materials science and medicine.