Obsidian is the most common form of natural glass and occurs in many attractive varieties. Since prehistoric times, people have used this material to make jewelry and carvings as well as practical objects, like knives.
Formed by volcanism, obsidian is considered a rock. It commonly occurs in large pieces, and lapidaries frequently cut them into cabochons, beads, and carvings. Faceted pieces tend to appear dark, except when cut in small sizes. These gems can make delicate jewelry stones.
Heat-sensitive obsidian has a hardness of 5-6 and brittle tenacity. As a result, cutting and wearing this material requires some care. However, the broken edges of these rocks are sharper than any steel knife. Cultures across the globe have made scalpels, arrowheads, knives, and scrapers from obsidians.
Transparent obsidians are quite rare, as are green, blue, and reddish colors. Hobbyists will occasionally facet these pieces. Obsidians can also display cat’s eyes. Although typically dark and opaque, obsidians come in many varieties popular with jewelry enthusiasts and mineral collectors.
This popular variety gets its name from its inclusions of snowflake-like spherulites of cristobalite. Jewelry makers frequently use these stones as beads and cabochons.
Beginning hobbyists often enjoy working with these cores of unaltered glass in nodular shells of decomposed obsidian. Commonly found in the southwestern American states of Arizona, Nevada, and New Mexico, some of these pieces have been faceted. This variety name comes from a legend of the Native American Apache people.
Mahogany obsidian, also known as mountain mahogany, is natural glass obsidian that has iron inclusions creating the mahogany colored stripes and swirls in it. Obsidian can be found anywhere volcanic activity has occurred.
Rainbow and Fire Obsidians
These varieties can show multiple brilliant colors due to inclusions of magnetite nano-crystals. The “fire” variety contains thinner layers of magnetite than the “rainbow” variety.
Color in obsidian varies, depending on impurities in the parent lava formation. Golden sheen obsidian is formed when patterns of gas bubbles are aligned along layers created by the flowing lava before it solidified.
Named after the Hawaiian goddess of volcanos and fire, this light, string-like volcanic basalt glass can actually become airborne. It can catch on trees and outdoor structures.
Black obsidian occurs in varying sizes north of Anahim Lake, on Anahim Peak and Ilgachuz Mountains.