Rock & Mineral Encyclopedia

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

Ironstone

An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.

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

Precious opal that forms in thin veins within brown ironstone boulders, cut with the host rock left as a natural dark backing.

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

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

Boulder opal from the Quilpie district of Queensland, Australia, with bright color set in dark ironstone matrix.

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