How Is Alexandrite Formed?

Chromium

For Alexandrite to form, chromium must be present in the rock formations before the natural heat and pressure process occurs. Alexandrite is one of three forms of chrysoberyl that are formed through volcanic heat and pressure. Without chromium, chrysoberyl crystals may still form, but they will not be Alexandrite and will not have the color-changing properties associated with Alexandrite.

Pressure

When pressure builds up within the earth, magma is pushed up toward the earth's crust. The magma travels through several layers of earth, including layers that contain both stone formations with chromium and water.

Heat

When the heat of the magma reaches the water and stone formations, it causes the water to evaporate and turn into steam. However, since the steam is trapped in the rock formation and cannot escape and return to the earth as water, it slowly cools along with the magma.

Cooling

As the water cools, minerals and elements contained in both the water and the magma combine and crystallize as the water expels these impurities. When high amounts of beryllium are in the magma, there is a chemical reaction that causes it to combine with the chromium in the rocks while crystallizing, creating a particular form of chrysoberyl known as Alexandrite. Other minerals present in the water, magma or surrounding rocks may also be incorporated into the Alexandrite crystal, affecting the color and clarity of the Alexandrite.

Resources

• Gemstone Education: Alexandrite