The Evolving Earth

From Crystal to Gem

Minerals, Crystals, and Gems: Revealing Earth's History

Minerals are solid inorganic materials with specific chemical compositions and distinct internal structures. When minerals form inside the earth, their atoms lock together to create crystals. Given sufficient space and other conditions, crystals can "grow" into a wide range of geometric forms with smooth surfaces. A mineral crystal's atomic arrangement depends not only upon its chemical composition but also upon external forces, thereby revealing aspects of our planet's history. For example, pure carbon commonly crystallizes as graphite, one of the softest of known minerals. But tremendous heat and pressure can transform carbon crystals so that they form diamonds, the hardest of all minerals. Gems are cut and polished mineral crystals prized for their beauty, durability, and rarity. We often stretch the definition of gem to include some beautiful and durable organic substances, like pearls, amber, jet, and coral.

Roll Out the Beryls

The colors of minerals and gems result from light interacting with the different atoms present in their crystals. The gems in this case are all varieties of the mineral beryl, composed of beryllium, aluminum, silicon, and oxygen. Beryl is colorless in its pure state. It acquires different colors when its crystals trap the atoms of different elements as they grow. Chromium, and more rarely vanadium, produce the vibrant green of emeralds. Aquamarine shows the variable tints of the sea because iron is present in its crystals. Red is the rarest of all varieties of beryl. The color results from the presence of manganese.

Emerald, Colombia	Emerald, North Carolina
Red Beryl, Utah	Aquamarine (beryl)

From Crystal to Gem
Azurite, Namibia	Barite, England	Dioptase, Namibia
Malachite, Zaire	Liddicoatite, Madagascar	Polished Septarian Nodule

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