Rock & Mineral Encyclopedia

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

Oolitic Limestone

Limestone built from tiny rounded ooid grains resembling fish roe, formed in warm, agitated shallow seas.

A rare agate that forms naturally with flat polygonal faces and angular geometric shapes rather than the usual rounded nodule.

Black volcanic glass crossed by a fine network of grey or brown veins that resemble a spider's web.

A mottled, multicolored obsidian blending black, brown, grey, and tan patches like a calico cat's patchwork coat.

A classic Oregon picture jasper showing layered tan, brown, and blue-grey scenes resembling desert landscapes and canyons.

An opaque grey-brown common opal forming nodules and concretions, historically called liver opal for its dull brownish color.