1 00:00:06,886 --> 00:00:11,216 Deep beneath the geysers and hot springs of Yellowstone Caldera 2 00:00:11,216 --> 00:00:16,184 lies a magma chamber produced by a hot spot in the earth’s mantle. 3 00:00:16,184 --> 00:00:19,077 As the magma moves towards the Earth’s surface, 4 00:00:19,077 --> 00:00:23,337 it crystallizes to form young, hot igneous rocks. 5 00:00:23,337 --> 00:00:27,392 The heat from these rocks drives groundwater towards the surface. 6 00:00:27,392 --> 00:00:32,882 As the water cools, ions precipitate out as mineral crystals, 7 00:00:32,882 --> 00:00:36,876 including quartz crystals from silicon and oxygen, 8 00:00:36,876 --> 00:00:41,886 feldspar from potassium, aluminum, silicon, and oxygen, 9 00:00:41,886 --> 00:00:45,126 galena from lead and sulfur. 10 00:00:45,126 --> 00:00:47,736 Many of these crystals have signature shapes— 11 00:00:47,736 --> 00:00:52,856 take this cascade of pointed quartz, or this pile of galena cubes. 12 00:00:52,856 --> 00:00:57,321 But what causes them to grow into these shapes again and again? 13 00:00:57,321 --> 00:01:00,013 Part of the answer lies in their atoms. 14 00:01:00,013 --> 00:01:04,933 Every crystal’s atoms are arranged in a highly organized, repeating pattern. 15 00:01:04,933 --> 00:01:08,508 This pattern is the defining feature of a crystal, 16 00:01:08,508 --> 00:01:10,518 and isn’t restricted to minerals— 17 00:01:10,518 --> 00:01:15,758 sand, ice, sugar, chocolate, ceramics, metals, DNA, 18 00:01:15,758 --> 00:01:19,679 and even some liquids have crystalline structures. 19 00:01:19,679 --> 00:01:22,459 Each crystalline material’s atomic arrangement 20 00:01:22,459 --> 00:01:25,699 falls into one of six different families: 21 00:01:25,699 --> 00:01:32,319 cubic, tetragonal, orthorhombic, monoclinic, triclinic, and hexagonal. 22 00:01:32,319 --> 00:01:34,359 Given the appropriate conditions, 23 00:01:34,359 --> 00:01:37,009 crystals will grow into geometric shapes 24 00:01:37,009 --> 00:01:39,699 that reflect the arrangement of their atoms. 25 00:01:39,699 --> 00:01:44,579 Take galena, which has a cubic structure composed of lead and sulfur atoms. 26 00:01:44,579 --> 00:01:46,622 The relatively large lead atoms 27 00:01:46,622 --> 00:01:50,932 are arranged in a three-dimensional grid 90 degrees from one another, 28 00:01:50,932 --> 00:01:55,662 while the relatively small sulfur atoms fit neatly between them. 29 00:01:55,662 --> 00:02:00,174 As the crystal grows, locations like these attract sulfur atoms, 30 00:02:00,174 --> 00:02:03,656 while lead will tend to bond to these places. 31 00:02:03,656 --> 00:02:07,096 Eventually, they will complete the grid of bonded atoms. 32 00:02:07,096 --> 00:02:11,236 This means the 90 degree grid pattern of galena’s crystalline structure 33 00:02:11,236 --> 00:02:14,593 is reflected in the visible shape of the crystal. 34 00:02:14,593 --> 00:02:17,973 Quartz, meanwhile, has a hexagonal crystalline structure. 35 00:02:17,973 --> 00:02:22,103 This means that on one plane its atoms are arranged in hexagons. 36 00:02:22,103 --> 00:02:27,564 In three dimensions, these hexagons are composed of many interlocking pyramids 37 00:02:27,564 --> 00:02:31,794 made up of one silicon atom and four oxygen atoms. 38 00:02:31,794 --> 00:02:34,171 So the signature shape of a quartz crystal 39 00:02:34,171 --> 00:02:39,571 is a six-sided column with pointed tips. 40 00:02:39,571 --> 00:02:41,691 Depending on environmental conditions, 41 00:02:41,691 --> 00:02:46,111 most crystals have the potential to form multiple geometric shapes. 42 00:02:46,111 --> 00:02:50,041 For example, diamonds, which form deep in the Earth’s mantle, 43 00:02:50,041 --> 00:02:56,261 have a cubic crystalline structure and can grow into either cubes or octahedrons. 44 00:02:56,261 --> 00:02:58,861 Which shape a particular diamond grows into 45 00:02:58,861 --> 00:03:01,151 depends on the conditions where it grows, 46 00:03:01,151 --> 00:03:05,451 including pressure, temperature, and chemical environment. 47 00:03:05,451 --> 00:03:09,128 While we can’t directly observe growth conditions in the mantle, 48 00:03:09,128 --> 00:03:11,868 laboratory experiments have shown some evidence 49 00:03:11,868 --> 00:03:15,838 that diamonds tend to grow into cubes at lower temperatures 50 00:03:15,838 --> 00:03:19,026 and octahedrons at higher temperatures. 51 00:03:19,026 --> 00:03:23,496 Trace amounts of water, silicon, germanium, or magnesium 52 00:03:23,496 --> 00:03:26,646 might also influence a diamond’s shape. 53 00:03:26,646 --> 00:03:31,256 And diamonds never naturally grow into the shapes found in jewelry— 54 00:03:31,256 --> 00:03:36,474 those diamonds have been cut to showcase sparkle and clarity. 55 00:03:36,474 --> 00:03:41,621 Environmental conditions can also influence whether crystals form at all. 56 00:03:41,621 --> 00:03:44,126 Glass is made of melted quartz sand, 57 00:03:44,126 --> 00:03:45,686 but it isn’t crystalline. 58 00:03:45,686 --> 00:03:48,706 That’s because glass cools relatively quickly, 59 00:03:48,706 --> 00:03:51,646 and the atoms do not have time to arrange themselves 60 00:03:51,646 --> 00:03:54,576 into the ordered structure of a quartz crystal. 61 00:03:54,576 --> 00:03:58,346 Instead, the random arrangement of the atoms in the melted glass 62 00:03:58,346 --> 00:04:00,906 is locked in upon cooling. 63 00:04:00,906 --> 00:04:03,546 Many crystals don’t form geometric shapes 64 00:04:03,546 --> 00:04:08,146 because they grow in extremely close quarters with other crystals. 65 00:04:08,146 --> 00:04:10,809 Rocks like granite are full of crystals, 66 00:04:10,809 --> 00:04:13,379 but none have recognizable shapes. 67 00:04:13,379 --> 00:04:15,539 As magma cools and solidifies, 68 00:04:15,539 --> 00:04:21,249 many minerals within it crystallize at the same time and quickly run out of space. 69 00:04:21,249 --> 00:04:23,881 And certain crystals, like turquoise, 70 00:04:23,881 --> 00:04:28,891 don’t grow into any discernible geometric shape in most environmental conditions, 71 00:04:28,891 --> 00:04:31,014 even given adequate space. 72 00:04:31,014 --> 00:04:34,204 Every crystal’s atomic structure has unique properties, 73 00:04:34,204 --> 00:04:39,134 and while these properties may not have any bearing on human emotional needs, 74 00:04:39,134 --> 00:04:44,204 they do have powerful applications in materials science and medicine.