Rock & Mineral Encyclopedia

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

Lignite

The lowest rank of coal, a soft brown carbon-rich rock formed from compacted peat, used mainly for electricity generation.

An iron-rich orthopyroxene prized for its warm bronze schiller, a metallic-looking sheen created by tiny mineral inclusions.

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

A soft pink common opal from the Peruvian Andes, prized for its opaque rosy color rather than play-of-color.

A limestone made of tiny spherical ooids, resembling fish roe, formed in warm, agitated shallow seas.

A patterned jasper whose bands and inclusions create miniature landscapes of deserts, mountains, and skies within the stone.

An opaque brown chalcedony whose iron-stained banding mimics deserts, dunes, and distant mountain skylines.

A clastic sedimentary rock made of cemented sand grains, often quartz, recording ancient beaches, deserts, and rivers.

A translucent chalcedony agate whose mineral inclusions form miniature scenes resembling mountains, trees, deserts, and skies.

A field term for hard black massive manganese oxides, often botryoidal, mined as an important manganese ore.

A jasper whose radiating mineral clusters form flower-like rosettes scattered across an earthy background.