Rock & Mineral Encyclopedia

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

Greywacke

A hard, dark, poorly sorted sandstone with a muddy matrix, typically deposited by underwater turbidity currents.

A treated chalcedony with a network of crackled veins, usually heated and dyed in vivid colors for affordable, eye-catching beads.

The most common variety of quartz, milky white from microscopic fluid and gas inclusions, forming massive veins worldwide.

Agate that forms in flat cracks or veins of host rock rather than rounded nodules, producing straight, parallel banding.

A pale jasper crossed by distinctive blue-gray veins or lines, valued by lapidaries for its calm color contrast.

A hollow rock nodule whose interior cavity is lined with inward-pointing crystals such as quartz, amethyst, or calcite.

A porous, spongy freshwater limestone that precipitates around springs, streams and lakes, often encrusting plants and moss.

A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.

A rounded sedimentary nodule cracked internally and filled with veins of yellow calcite, prized for its striking dragon-skin patterning.

Agate found in the gravels of Crowley's Ridge in northeastern Arkansas, a stream-transported banded chalcedony.

Siderite is an iron carbonate ore, a brown rhombohedral mineral of the calcite group found in sediments and veins.

A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.

Quartz with a wider crystal 'cap' that grew over a narrower stem, forming a natural scepter or mushroom shape.