Rock & Mineral Encyclopedia

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

Sandstone

A clastic sedimentary rock made of cemented sand grains, often quartz, recording ancient beaches, deserts, and rivers.

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

A black-and-white striped chalcedony-quartz rock whose bold zebra-like banding makes it a popular ornamental and lapidary stone.

A soft, fine-grained, porous white limestone made largely of microscopic calcareous plankton skeletons, the rock that forms classic white cliffs.

A poorly sorted, muddy sandstone with abundant clay matrix between its grains, typically dark and deposited by turbidity currents.

A coarse-grained mafic plutonic rock similar to gabbro but with orthopyroxene as the dominant pyroxene instead of clinopyroxene.

A very fine-grained limestone made of microcrystalline calcite mud, dense and smooth, deposited in calm carbonate settings.

A famous white to blue-grey Italian marble from Carrara, prized for centuries by sculptors and architects for its purity and fine grain.

Green tourmaline cut as a cabochon to show a sharp moving band of light (chatoyancy) caused by fine parallel inclusions.

A hard, tough metamorphic rock of fused quartz grains, formed by recrystallizing quartz sandstone under heat and pressure.

A banded agate that diffracts transmitted light into rainbow colors when cut thin and backlit, producing a spectacular iridescence.

A finely banded agate from Botswana known for delicate parallel layers of grey, pink, and white.