Rock & Mineral Encyclopedia

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

Mocha Agate

A pale translucent chalcedony threaded with brown-black manganese and iron dendrites that mimic tiny ferns, mosses or landscapes.

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.

A yellow-brown alteration material formed when basaltic volcanic glass reacts with water, common in hydrovolcanic tuffs and pillow lavas.

Glacially deposited banded agates found along Lake Michigan beaches, small waterworn pebbles with concentric red and grey banding.