Obsidian Rock Type, Composition, Formation, Occurrence & Uses

Obsidian Rock
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Obsidian is an igneous rock. It is an amorphous material, commonly known as a mineraloid. The rock is formed when molten rock material cools so rapidly that atoms don’t get time to arrange themselves in a crystalline structure. It results in volcanic glass with a smooth and uniform texture that breaks with a conchoidal feature.

Obsidian is usually found in black color. Some color variations include brown, tan, and green. Obsidian can rarely be blue, red, orange, or yellow. The color variations are usually caused by trace elements or minerals. You may find two colored obsidian rocks such as black and brown. This variant is commonly known as “mahogany obsidian.”

Obsidian rock
Obsidian rock

Rock Composition

Obsidian’s composition is pretty similar to rhyolite and granite. The common and abundant components include SiO2 (silica), MgO, and Fe2O3. These components are often responsible for the color changes in the rock. Aluminum oxide content is lower than rhyolite and granite.

Obsidian Rock Formation

Obsidian mostly solidifies above the earth’s surface (extrusive). It forms along the edges of a lava flow, edges of a volcanic dome, and lava cooling sites. It can also form in intrusive rock settings around the edges of a sill or a dike. It is also formed around the edges of a sill or dike (intrusive settings).

Where is Obsidian Found?

Obsidian is present in large quantities all around the world, but it is confined to areas of geologically recent volcanic activity. The problem with this rock is that it is quickly damaged by weathering, heat, or other climatic events.

Obsidian is found in large quantities in North America, Argentina, Chile, Greece, Ecuador, Hungary, Iceland, Indonesia, Italy, Japan, Kenya, Peru, Russia, and Japan.

The United States has large obsidian reserves as well. It is found in many locations like Arizona, California, Idaho, Nevada, New Mexico, Oregon, Washington, and Wyoming. Most obsidian used in jewelry is produced in the US.

Obsidian talus at Obsidian Dome, California
Obsidian talus at Obsidian Dome, California

Obsidian Uses

Obsidian has been used in prehistoric and historical times as a cutting tool. Recent discoveries have shown that people in the stone age used obsidian to make arrowheads, spears, knife blades, and scrapers.

Modern-day uses include using obsidian as a cutting tool in surgeries. Obsidian is used to make cutting tips that are thinner and sharper than high-quality surgical steel. These blades are used in scalpels for complicated surgeries.

Obsidian is shaped into beads, cabochons, and tumbled stones to make jewelry items. It is polished and processed to make highly reflective beads. However, the jewelry items made using obsidian are not very durable.

Obsidian arrowhead
Obsidian arrowhead

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