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.

Ancient wood whose organic tissue has been replaced by silica, preserving the grain, rings, and structure of the original tree in stone.

A lightweight black organic gemstone formed from fossilized wood under pressure, a type of lignite long used in mourning jewelry.

Fossilized tree resin, warm and lightweight, sometimes preserving ancient insects and plant matter inside.

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.