Rock & Mineral Encyclopedia

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

Metaconglomerate

A conglomerate altered by heat and pressure, often with its rounded pebbles stretched and flattened into elongated lenses.

A general field term for green, low-grade metamorphosed basaltic rocks colored by chlorite, epidote, and actinolite.

Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.

A yellow-brown alteration material formed when basaltic volcanic glass reacts with water, common in hydrovolcanic tuffs and pillow lavas.

A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.

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

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.