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Gemstone Origins
Modified: April 2011
by Doug Floyd
Treasured by all races and religions, gemstones have captured the imagination of humans for thousands of years. During that time, gemstones have been credited with powers of protection, healing, wisdom--even invisibility and life. But where do gemstones come from?
Most gemstones are actually mineral crystals (except for nonmineral, organic gems like pearls, coral, and amber). Mineral crystals form through a naturally occurring combination of chemicals, heat, and/or pressure. These chemicals affect the shape and color of the crystals. Most mineral crystals are tiny, but a few grow large and fine enough to be cut into gemstones of rare beauty. Those gemstones are the crowning glory of the mineral world.
While we don't consciously think about them, minerals play an important role in our everyday lives. They form the rocks in the earth's crust, and they fill our homes, our highways, and even our cars. (To learn a little more about minerals, research the U.S. Geological Survey for an interesting fact file.)
Mineral crystals form during one of three rock-making processes and, therefore, fall into one of three categories: igneous rocks, sedimentary rocks, and metamorphic rocks.
Igneous Rocks
Deep within the earth's inferno brews a stew of molten rock and gases called magma. As magma wells up within the earth, intense pressure builds, forcing the liquid rock toward the surface--sometimes breaking through as lava. It slowly cools to form igneous rocks, and within these rocks and gas-bubble spaces, interlocking crystals grow. The minerals present, the cooling time, and the environment all play a role in the way these crystals form. Examples of gemstones found in igneous rock include diamond, topaz, kunzite, and spinel.
Sedimentary Rocks
Rock fragments near the earth's surface are often washed into riverbeds and seabeds. Over time, layers of rock fragments, mud, and other organic and inorganic elements are compacted together into hard rock. Sometimes sea creatures, bugs, or other organic elements will get trapped within these rock formations. Examples of sedimentary rocks include limestone, shale, and sandstone. Surprisingly, most gemstones are found in sedimentary deposits. Discovered in riverbeds, these alluvial deposits include gems such as sapphire and ruby.
Metamorphic Rocks
Intense pressure and high temperatures can actually cause recrystallization, transforming the composition of the rock. This happens deep within the earth's crust, and it can also happen through direct contact with hot magma. Emerald sometimes forms in hydrothermals associated with magma. Other examples of metamorphic gemstones include jadeite and peridot.
In each of the above cases, crystals grow as atoms to form a complex yet ordered structure. The structure and the mineral's chemical composition combined form the crystal's properties, such as shape, hardness, cleavage, refractive index, and more.
