How Do Aquamarine Gemstones Form?

Aquamarine is called "the water of the sea" because of its characteristic sea-blue color.

Aquamarine is a blue variety of beryl. Beryl is a silicate mineral often found in granitic rocks that is usually clear. Trace amounts of iron present during the crystal's growth provide the aquamarine with its unique color and make it a valuable gemstone.

Fiery Birth

The Rocky Mountains are just one source of aquamarine gemstones.

Aquamarine is commonly found in Colorado and Utah, among the Rocky Mountains. The Rocky Mountains were formed millions of years ago by volcanic activity. The intrusion of magma into the continental crust melted the existing rock, creating new formations of basalt and granite.

Cooling

The magma that formed the Rocky Mountains took several million years to cool completely. Pegmatitic granite, a type of granite that contains large crystals, is one kind of igneous rock that resulted. Pegmatitic granite forms when liquid minerals are still present in the surrounding rock. Crystals slowly form as the mineral's atoms come together and become a solid, much like liquid water becoming ice.

Metamorphosis

Crystal growth can continue in, and is often enhanced by, the ongoing heat and pressure present deep in the earth. The longer the crystal is subjected to these conditions, the more likely it is to be altered in some way. Whether or not the crystal undergoes metamorphic changes depends on the conditions at its location. Longer cooling times also result in larger crystals. One single specimen of aquamarine was over 18 feet long.

References

• Emporia State University: Gemstones and Gemology
• University of Texas: Beryl Gem Notes
• PBS: A Primer on Gemstones