Rock & Mineral Encyclopedia

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

Sapropel

A soft, dark, organic-rich mud deposited in stagnant, oxygen-poor water, a key precursor to oil and gas source rocks.

A water-bearing massive grossular garnet, usually green or pink, widely used as a tough jade-like carving stone.

A vivid green chromium-bearing diopside, an affordable emerald-like gem mined largely in Siberia.

A pale jasper threaded with black, fern-like mineral dendrites that mimic plants, trees, and frost despite being inorganic.

A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.

A black-and-white striped chalcedony-quartz rock whose bold zebra-like banding makes it a popular ornamental and lapidary stone.

A high-grade metamorphic rock formed in the deep, hot crust, marked by anhydrous minerals like pyroxene and garnet.

A hard, fine-grained siliceous rock with a dull porcelain-like texture, intermediate between soft diatomite and dense chert.

An earthy aluminum-rich residual rock and the world's principal ore of aluminum, often showing distinctive pea-like pisolites.

A dark, foliated schist rich in needle-like hornblende crystals, formed by metamorphism of mafic igneous rocks.

A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.

A lustrous black titanium-rich garnet of the andradite series, found in alkaline igneous rocks like nepheline syenite and ijolite.