Rock & Mineral Encyclopedia

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

Diabase

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

A calcium-magnesium carbonate mineral and rock similar to limestone but harder and only weakly reactive to acid.

A mafic volcanic rock speckled with pale spherical 'varioles,' typically formed in rapidly chilled basaltic pillow lavas.

A fine-grained, sodium-rich contact-metasomatic rock formed where shale is albitized next to intruding diabase or spilite.

A pale jasper crossed by distinctive blue-gray veins or lines, valued by lapidaries for its calm color contrast.

A soft metamorphic rock made of talc and magnesite or dolomite, formed by hydrothermal alteration of ultramafic rocks.

A metamorphosed limestone of interlocking calcite crystals, prized for sculpture and architecture for its workability and polish.

A marbled, abstractly patterned stone resembling modern art, technically a metamorphosed limestone rather than a true silica jasper.

A rare igneous rock made mostly of carbonate minerals, source of the world's most important rare-earth-element and niobium deposits.

A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.