Rock & Mineral Encyclopedia

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

Seam Agate

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

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

A dark, foliated schist rich in graphite that leaves a grey-black mark and forms from metamorphosed carbon-rich sediments.

A dark hornblende-rich lamprophyre dike rock with amphibole and augite phenocrysts in an alkali-feldspar-dominated groundmass.

A warm mustard-to-ochre yellow jasper colored by iron, valued by lapidaries for its rich, earthy golden tone.

A pink, manganese-rich variety of zoisite used as an ornamental gemstone, often mottled with white quartz and grey matrix.

A feldspar-rich sandstone, often pink, that points to granitic source rocks eroded quickly in dry or cold climates.

A sodium-rich alkali feldspar of sodic volcanic rocks, sometimes forming large glassy crystals and the blue-flashing feldspar in larvikite.

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

A rare strontium-dominant feldspar, the strontium analogue of paracelsian, found in metamorphosed strontium-rich and manganese-bearing rocks.

A mica schist containing bladed blue kyanite crystals, a marker of medium- to high-grade metamorphism of aluminous rocks.

Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.

A richly colored red banded agate prized by lapidaries for its deep crimson-to-brown tones reminiscent of pigeon's blood.

A hard zinc-rich member of the spinel group, usually dark blue-green to black, forming octahedral crystals in metamorphic and pegmatitic rocks.