Sapphires are the most common colored gemstone, preceded in popularity only by the diamond. Their rich blue hue and rarity have made them a treasured gemstone. They form under very specific conditions in the earth.
Like rubies, sapphires are also formed out of the mineral corundum. Corundum acquires color when there are other minerals that become present as it is forming. When corundum takes on a hue other than red, the gemstone is typically classified as sapphire. Thus, there are many color varieties in sapphire including pink, yellow and most popularly blue. With iron present, the sapphire can take on a yellow color. With vanadium, purple sapphires are created. And most popular, the blue sapphire is created as a result of titanium being present. Corundum is found in igneous rocks. When those are cooling slowly, large crystals of minerals can form. The more slowly the magma cools, the larger the sapphires will be. Sapphires are typically found in recrystallized limestone and metamorphic rocks that have less silica and a lot of aluminum.
Sapphire is a remarkably hard mineral at 9 on the Mohs scale, preceded only by moissanite and diamond. This dense gemstone is a durable choice to craft jewelry for many decades.
Sapphire deposits can be found in Myanmar, Sri Lanka, Madagascar, and Kashmir as well as Montana. Sapphires from different locations can have different chemical properties as well as differing microscopic inclusions.
The crystallization of a sapphire is divided into two phases, a nucleus forms and subsequent layers of mineral are added over time. During the formation of a sapphire rutile inclusions can form. These rutile inclusions look like small crystalline growths inside of the sapphire. Almost all sapphires have inclusions. Natural sapphires can be distinguished from synthetic sapphires by their inclusions. The majority of natural sapphires are heat treated to improve their color. This treatment is permanent. Natural sapphires that are free of inclusions are immensely rare and carry a premium price tag.