OBSIDIAN ROCK INFORMATION

Obsidian is a naturally occurring volcanic glass formed when lava cools so quickly that crystals don’t have time to grow. The result is a smooth, glassy, extremely sharp rock with a long human history and striking visual variety.

What Obsidian Is
Obsidian is an igneous rock created from rapidly cooled felsic lava, rich in silica (SiO₂). Because it cools so fast, it becomes amorphous—a glass rather than a crystalline mineral.

Key traits:

Volcanic glass with a smooth, vitreous texture

Conchoidal fracture that produces razor‑sharp edges

Hardness: 5–6 on the Mohs scale

Color: usually black, but can be brown, green, red, yellow, or even iridescent depending on impurities

How Obsidian Forms
Obsidian forms when high‑silica lava cools extremely fast—often at the edges of lava flows, volcanic domes, dikes, or when lava meets water or air. The high viscosity of the lava prevents crystal formation, locking it into glass.

Types and Variants
Obsidian comes in many visually distinct varieties, each shaped by trace elements or inclusions:

Black Obsidian — the classic deep‑black glass

Mahogany Obsidian — black with reddish‑brown swirls

Rainbow Obsidian — iridescent colors from microscopic crystals

Snowflake Obsidian — white/gray spherulites resembling snowflakes

Historical and Modern Uses
Because of its sharpness and workability, obsidian has been used for:

Cutting tools and weapons by ancient cultures (Aztec, Greek, Native American)

Mirrors and ornaments

Experimental surgical blades, which can be sharper than steel

Where Obsidian Is Found
Obsidian occurs in volcanic regions worldwide. Well‑known sources include:

Mount Hekla, Iceland

Eolie Islands, Italy

Obsidian Cliff, Yellowstone (USA)

where does the name come from
Short answer: The name obsidian comes from a Roman named Obsius, who was said to have discovered the stone in Ethiopia. The Latin term lapis obsidianus (“Obsius’s stone”) eventually became obsidianus, then obsidian in English.

Where the name actually comes from
The story traces back to Pliny the Elder, a Roman author who wrote Naturalis Historia. In it, he mentions a volcanic glass called “obsidianus lapis”, named after Obsius, a Roman traveler who supposedly found the material in Ethiopia. Over time:

lapis obsianus → “stone of Obsius”

A manuscript error changed obsianus to obsidianus

English adopted obsidian in the 1600s

This is why the modern word looks slightly different from the original Latin.