April: Month of Diamond

October 21, 2002
Burke Museum
A cut diamond set between sapphires.

Photo: “Diamond Macro 3” by Stephen Durham is licensed under CC BY-ND 2.0.

Kimberlite is the ancient volcanic rock in which diamonds are found.

Photo: “Diamond in kimberlite” by James St. John is licensed under CC BY-ND 2.0.

Quartz crystal is an alternate birthstone for April.

Photo: “Quartz Cluster” by Mark, Vicki, Ellaura and Mason is licensed under CC BY-ND 2.0.

History of diamond

Diamond is the most familiar gemstone and it has a rich and interesting history. Diamonds are known for their prismatic beauty and hardness, and they are highly valued for these and other qualities. At one time, it was even thought that if you took a diamond into bed with you, it would cure your illness!

Science of diamond

Diamond is a form of carbon with a tightly bound crystalline structure. It originates deep inside the Earth under intense pressure and high temperatures. Diamonds are brought up to the surface by very deep-seated volcanic activity. Diamond-bearing volcanoes are called kimberlies, and they erupted millions of years ago.

Interestingly, both graphite (used in pencils) and diamond are forms of carbon, but they have very different structures and properties: graphite is opaque and soft, while diamond is transparent and the hardest mineral on Earth. These differences occur because diamond crystallizes in the isometric system while graphite crystallizes in the hexagonal system.

Group: Carbons
Class: Native Elements
Subclass: Non-metallics
Chemistry: C, elemental carbon

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Emeralds are a variety of the mineral beryl, shown here in its uncut state.

Emerald is another variety of beryl. It is surprisingly common for emeralds to contain flaws and veins of chemicals called inclusions.

Aquamarine gems are a clear blue-green color.

Aquamarine is a variety of the mineral beryl. Beryl generally forms inside granites as magma (molten rock) cools deep inside the Earth.

Citrine as naturally occurring crystals.

Some citrine actually began as purple amethyst, but heat from nearby molten rock changed it to a warm yellow color.

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