Rock & Mineral Encyclopedia

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

Bituminous Shale

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

A fine-grained sedimentary rock rich in solid organic matter (kerogen) that yields oil and gas when heated.

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

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

Hardened, fine-grained mudrock intermediate between shale and slate, dense and non-fissile, often carved into ornaments.

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

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

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

A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.