What Is Obsidian? Black, Snowflake and Rainbow Obsidian Explained

Short answer: obsidian is natural volcanic glass. It forms when silica-rich lava cools so quickly that crystals cannot grow. It is usually glossy black, and its varieties include snowflake obsidian with white spots, rainbow and fire obsidian with iridescent bands, golden sheen obsidian and mahogany obsidian streaked with reddish brown. Obsidian breaks into razor-sharp edges, and for thousands of years people made blades, arrowheads and mirrors from it. In crystal traditions it is a classic protection and grounding stone.

What is obsidian?

Obsidian is an igneous rock made of glass rather than crystals. It is rich in silicon, oxygen, aluminum, sodium and potassium, the same elements as granite and rhyolite, which are the crystalline rocks of similar composition. Because it is glass, with no crystal structure and a variable composition, it is not a true mineral; it is sometimes classified as a mineraloid. It is mostly silicon dioxide, usually 70 percent or more.

Obsidian rates about 5 to 6 on the Mohs scale, softer than quartz, and has a specific gravity of about 2.4. It has a glassy luster and breaks with a smooth, curved, shell-like (conchoidal) fracture.

How does obsidian form?

Obsidian forms from felsic lava, lava with a high content of silica. That makes the lava very thick and sticky. The thick lava slows the movement of atoms, which stops crystals from starting to form, and when it also cools quickly, the result is natural glass. Obsidian is commonly found at the edges of rhyolite lava flows, called obsidian flows, and of volcanic domes.

Obsidian does not last forever. Over geological time the glass slowly turns into fine-grained crystals, a process called devitrification, and water speeds it up. That is why obsidian older than the Miocene, about 23 million years, is rare.

Why is obsidian black?

Iron and other elements give obsidian a dark brown to black color, and most black obsidian contains tiny particles of magnetite, an iron oxide. Very few samples are nearly colorless.

What are the types of obsidian?

• Black obsidian: the classic glossy black volcanic glass.
• Snowflake obsidian: black glass with small white, radiating clusters of the mineral cristobalite, which look like snowflakes.
• Sheen obsidian: layers of tiny gas bubbles, left from the flowing lava, produce a golden or silver sheen.
• Fire obsidian: an iridescent, rainbow-like sheen from magnetite nanoparticles that create thin-film interference.
• Rainbow obsidian: colorful striped obsidian from Mexico, colored by oriented nanorods of the mineral hedenbergite, again through thin-film interference.
• Mahogany obsidian: black glass with reddish brown patches and wood-grain streaks from iron oxides such as hematite.
• Apache tears: small rounded obsidian nuggets, often found embedded in grayish white perlite.

Green, brown, and rarely yellow, orange, red or blue obsidian also occur.

Obsidian vs moldavite and glass

Obsidian and moldavite are both natural glasses, but they formed differently: obsidian from volcanic lava, moldavite from rock melted by a meteorite impact. Tektites such as moldavite contain far less water than volcanic glass.

Natural obsidian is usually black, sometimes green or brown, and only rarely yellow, orange, red or blue, so be cautious with brightly colored "obsidian" and ask what it is.

A stone that made history

Obsidian's sharp edges made it one of the most important materials of the Stone Age. Like all glass, it breaks with a conchoidal fracture, so it can be shaped by knapping into blades and points.

• Tools and trade: the earliest known use, at Kariandusi in Kenya and other early Stone Age sites, dates to about 700,000 BC. By the late Neolithic, obsidian bladelets made on the island of Lipari were traded as far as Sicily, northern Italy and Croatia.
• Mirrors: obsidian was polished into early mirrors. The English scholar John Dee owned an obsidian mirror brought from Mexico to Europe after the Spanish conquest.
• Mesoamerica: green obsidian from Pachuca, Mexico, was highly prized, and has been argued to have been controlled by the city of Teotihuacan.
• Trade across North America: obsidian from the Yellowstone region has been found at Hopewell sites in Ohio, more than 1,500 miles away.
• Today: obsidian has been tested experimentally as surgical scalpel blades, since its fractured edge can be extremely sharp.

The Roman writer Pliny the Elder described a volcanic glass he called lapis obsidianus, said to have been found in Ethiopia by a man named Obsidius, and that is where the name comes from.

Where is obsidian found?

Obsidian is found wherever there has been silica-rich volcanic activity. In the United States it occurs in Yellowstone National Park, at Inyo Craters in California, in the Cascade Range and in many other western states, including Arizona, Colorado and New Mexico. Mexico is a major source of rainbow and other colored obsidian.

What is obsidian traditionally associated with?

In modern crystal traditions, black obsidian is one of the best-known protection stones, associated with shielding against negativity, grounding and honest self-reflection, a meaning that echoes its long use as a mirror. It is commonly linked with the root chakra and often named as a stone for Scorpio and Capricorn. Snowflake obsidian is associated with balance, and rainbow obsidian with hope.

These are traditions and beliefs. They are part of why people choose obsidian, not properties you can measure in the stone.

Raw, tumbled and polished obsidian

Rough obsidian shows sharp, curved fracture surfaces and should be handled carefully. Polished obsidian is made into spheres, hearts, palm stones, towers, pyramids and tumbles, and polishing brings out sheen and rainbow effects, which are best seen when the stone is cut in the right direction.

Can you wear obsidian?

Yes, as pendants, beads and earrings. At 5 to 6 on the Mohs scale it is softer than quartz and brittle, so obsidian rings and bracelets can scratch and chip with knocks.

How do you care for obsidian?

• Handle rough pieces carefully. Freshly broken obsidian edges can be extremely sharp.
• Wash it with warm water and mild soap, then dry it.
• Store it apart from harder stones, which can scratch it.
• Avoid drops and sudden knocks. Obsidian is glass and can chip or shatter.

How can you tell real obsidian?

• Fracture: natural obsidian breaks with smooth, curved, shell-like surfaces.
• Color and inclusions: natural obsidian is mostly black, sometimes green or brown, often with layered bubbles, snowflake spherulites or sheen. Bright colors are rare in nature, so ask about them.
• Hardness: obsidian is softer than quartz, so quartz will scratch it.

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Frequently asked questions

Is obsidian a crystal?

No. Obsidian is natural volcanic glass with no crystal structure. It is sometimes classified as a mineraloid and is sold alongside crystals.

What is snowflake obsidian?

Black obsidian with small white, radiating clusters of the mineral cristobalite that look like snowflakes.

What causes the colors in rainbow obsidian?

Tiny, aligned nanorods of the mineral hedenbergite inside the glass create thin-film interference, which shows as rainbow bands.

What is black obsidian traditionally associated with?

In crystal traditions it is associated with protection, grounding and self-reflection, and linked with the root chakra. These are traditional meanings rather than measurable properties.

Can obsidian go in water?

Yes. Obsidian can be washed with mild soap and water. Dry it afterward.

Is obsidian sharp?

Freshly broken obsidian can be extremely sharp. That is why it was used for blades for thousands of years. Polished pieces are smooth and safe to handle.

Sources

• Wikipedia, Obsidian: https://en.wikipedia.org/wiki/Obsidian
• Wikipedia, Tektite: https://en.wikipedia.org/wiki/Tektite
• FossilEra, Mahogany obsidian: https://www.fossilera.com/fossils-for-sale/mahogany-obsidian