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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.

obsidian British  
/ ɒbˈsɪdɪən /

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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.

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

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

From The Wall Street Journal • Jan. 16, 2026

“All is fair where you wear the crown,” snipes Gal Gadot’s evil queen, who wears slinky ballgowns made of obsidian shards that clatter and clank with every step.

From Los Angeles Times • Mar. 19, 2025

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

It spread its metal wings, blinked its obsidian eyes, and flew around the room.

From "The Battle of the Labyrinth" by Rick Riordan

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.