Rock & Mineral Encyclopedia

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

Sardonyx

A banded chalcedony combining reddish-brown sard with white or black onyx layers, prized since antiquity for carved cameos.

A deep black variety of banded chalcedony, often closely related to or treated like onyx, used for jewelry and carvings.

A banded variety of chalcedony quartz, classically black or black-and-white, long favored for cameos and beads.

A metamorphosed banded iron formation of alternating quartz and iron-oxide layers, mined as a major iron ore.

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

A soft, fine-grained, translucent form of gypsum (or banded calcite) long prized as a carving and ornamental stone.

A banded, metamorphosed iron formation in which bright red jasper alternates with silvery hematite or magnetite layers.

Glacially transported banded agates found along Lake Huron's shores, typically small, frosted pebbles with red-orange iron banding.

A vivid yellow-and-black banded stone from Indonesian volcanic vents, colored by sulfur, arsenic minerals and iron oxides, not true jasper.

Obsidian colored brown by iron oxide inclusions, frequently banded or swirled with black as in mahogany obsidian.

A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.

A banded agate whose internal structures resemble cathedral spires, arches, or a city skyline of towers and pinnacles.

A banded agate that displays a moving shadow or flash across its surface when tilted under light, caused by closely spaced parallel bands.