Rock & Mineral Encyclopedia

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

Eclogite

A dense, high-pressure metamorphic rock famous for its red garnets set in bright green pyroxene, formed deep within subduction zones.

An intermediate plagioclase feldspar between albite and anorthite, marketed as a red to champagne gemstone, sometimes color-treated.

A warm orange-to-red variety of chalcedony quartz colored by iron oxide, used since antiquity for seals, beads, and cabochons.

The red, chromium-colored variety of corundum, prized as one of the most valuable colored gemstones and second only to diamond in hardness.

A mica schist studded with red-brown staurolite porphyroblasts, including the famous cross-shaped twins called fairy stones.

A rare garnet that dramatically shifts color from greenish in daylight to reddish under lamplight, rivaling alexandrite.

A solid jet-black chalcedony, usually a dyed and treated agate, prized for sleek polished beads, cabochons, and intaglios.

A manganese aluminum garnet glowing in vivid orange to reddish-orange tones, with the finest called mandarin garnet.

An earthy-toned jasper with vine-like or scenic patterning, valued by lapidaries for warm browns, reds, and creams that polish to a smooth finish.

A glacier-transported banded agate from the Lake Superior region, colored by iron into rich reds and oranges, and Minnesota's state gemstone.

A fractured and re-cemented agate whose angular broken bands resemble crumbling walls and ruined cityscapes when polished.