Rock & Mineral Encyclopedia

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

Basalt

A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.

A coarse-grained, dark mafic intrusive rock that is the plutonic equivalent of basalt, rich in plagioclase and pyroxene.

A tough, fine-grained, non-foliated rock formed by the intense heat of nearby magma baking surrounding rock at contact zones.

A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.

A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.

A tough, fine-grained contact-metamorphic rock containing cordierite, often spotted, formed by heat from nearby igneous intrusions.

A dark, dense metamorphic rock dominated by hornblende and plagioclase, formed by medium- to high-grade metamorphism of basalt.

A fine-grained, intermediate volcanic rock common at subduction-zone volcanoes, between basalt and rhyolite in composition.

A fine-grained foliated metamorphic rock between slate and schist, recognized by its silky silvery sheen and wavy, crinkled surfaces.

Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.

A dark, organic-rich shale loaded with kerogen and bitumen that can yield oil and gas, often finely laminated and combustible.

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

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

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