Rock & Mineral Encyclopedia

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

Bone Opal

Fossil bone in which opal has replaced the original tissue, sometimes showing play-of-color, a rare collector fossil.

Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.

Extremely fine-grained, even-textured limestone famous for lithographic printing and for preserving exquisite fossils like Archaeopteryx.

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

A transparent, colorless opal that looks like water or jelly, sometimes flashing subtle play-of-color from within.

A water-bearing massive grossular garnet, usually green or pink, widely used as a tough jade-like carving stone.

A translucent, gelatinous-looking opal whose transparency gives floating, glowing play-of-color a watery, jelly-like appearance.