obsidian

American  

[uhb-sid-ee-uhn] / əbˈsɪd i ən /

noun

1. a volcanic glass similar in composition to granite, usually dark but transparent in thin pieces, and having a good conchoidal fracture.

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obsidian British  

/ ɒbˈsɪdɪən /

noun

1. Also called: Iceland agate.  a dark volcanic glass formed by very rapid solidification of lava

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obsidian Scientific  

/ ŏb-sĭd′ē-ən /

1. A shiny, usually black, volcanic glass. Obsidian forms above ground from lava that is similar in composition to the magma from which granite forms underground, but cools so quickly that minerals do not have a chance to form within it.

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Etymology

Origin of obsidian

First recorded in 1350–1400; from Latin Obsidiānus, printer's error for Obsiānus “pertaining to Obsius,” the discoverer (according to Pliny) of a similar mineral in Ethiopia; replacing Middle English obsianus, from Latin

Explanation

Obsidian is a type of black or dark glass formed from cooling lava. So if you find a shiny, hard, dark piece of glass next time you’re hanging around a volcano, it’s probably a piece of obsidian. The word obsidian essentially means “stone of Obsius.” So who was Obsius? According to an ancient Roman writer, he was the guy who first found this type of stone in Ethiopia. You’ll find obsidian used as a modifier a lot. Think of an obsidian arrowhead, blade or mirror. Sometimes it is used as a fancy way of describing people’s eyes in romance novels as in, “Her eyes were dark and shining, two obsidian orbs.”

Example Sentences

From precolonial Mexico we discover obsidian mirrors used for divination in Mayan and Aztec ceremonies.

From The Wall Street Journal • Jan. 16, 2026

Like obsidian, in fact, their edges are sharp but the shards have an almost twirly shape and lack the crystalline structure of black-colored minerals like augite or tourmaline.

From Salon • Mar. 4, 2025

One gem is thought to be a rare, 2nd Century head of the Greek hero Hercules made from obsidian, a type of volcanic glass.

From BBC • May 27, 2024

The Cahuilla also charted trade corridors reaching from the Colorado River to the shores of the Pacific, where coastal tribes traded shell jewelry for obsidian tools and animal skins from the interior.

From Los Angeles Times • Apr. 28, 2024

I hold up my pendant to the sky, centering the dwarf sun in the middle of the obsidian.

From "The Last Cuentista" by Donna Barba Higuera

Related Words

• sunless
• unlighted
• unlit