Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Black Obsidian

Jet-black natural volcanic glass formed by rapidly cooled lava, prized for its glassy luster and razor-sharp conchoidal fracture.

Obsidian that has partly crystallized over time, growing pale spherulite clusters within the black glass, as in snowflake obsidian.

A black volcanic glass speckled with gray-white cristobalite snowflakes, formed as obsidian begins to crystallize.

Black volcanic glass dotted with radiating spherulite bursts that look like exploding fireworks frozen in the stone.

Obsidian formed from two merged lava flows, producing a stone with two distinct bands of sheen or color.

A dull, resinous volcanic glass similar to obsidian but with higher water content and a waxy pitch-like luster.

A hydrated volcanic glass with pearly, onion-like concentric cracks that pops into lightweight white granules when heated.

A hard, dark variety of chert that knaps into razor-sharp edges and sparks against steel, central to Stone Age technology.

Ancient wood whose organic tissue has been replaced by silica, preserving the grain, rings, and structure of the original tree in stone.