Rock & Mineral Encyclopedia

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

Erythrite

A soft pink to crimson hydrated cobalt arsenate, famous as cobalt bloom that signals nearby cobalt ores.

A vivid blue-green hydrated copper silicate, soft on its own but prized as a gem when hardened by intergrown quartz or chalcedony.

A metallic cobalt-nickel arsenide, an important cobalt ore, named for the Skutterud mines of Norway.

Opal without play-of-color, valued for solid body hues; also called potch, it occurs in a wide range of colors worldwide.

A durable magnesium aluminum oxide gem that occurs in many colors and was long mistaken for ruby.

A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.

Obsidian with a vivid blue sheen or hue; natural blue obsidian is rare, and intensely uniform blue material is usually manufactured glass.

A man-made glittering glass colored deep blue with cobalt and studded with tiny copper crystals that mimic a starry night sky.

A banded, metamorphosed iron formation in which bright red jasper alternates with silvery hematite or magnetite layers.

Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.

The highest-rank coal, a hard, lustrous black rock that burns cleanly with little smoke and high heat output.