Rock & Mineral Encyclopedia

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

Loess

A loose, wind-blown silt deposit, typically buff-colored and very fertile, that forms thick blankets and stands in steep cliffs.

A glittery, strongly foliated rock made mostly of aligned mica flakes that split into thin, shiny sheets.

A transparent, optical-grade variety of calcite famous for strong double refraction, splitting images and light into two rays.

A deep, rich forest-green elbaite tourmaline (verdelite) colored mainly by iron, with strong pleochroism and excellent durability.

The gem variety of cordierite, famous for strong pleochroism that shifts from violet-blue to near-colorless.

A naturally magnetic black iron oxide and a major iron ore; strongly magnetic specimens are known as lodestone.

An extremely common calcium carbonate mineral that comes in nearly every color and shows strong double refraction in clear crystals.

The delicate pink-to-lilac variety of spodumene, a lithium silicate prized for soft color and strong pleochroism but tricky perfect cleavage.

A fine-grained, strongly foliated rock formed deep in fault zones where rocks flowed and ground down rather than fracturing.

A classic Oregon plume agate from the Priday Ranch beds, showing feathery mineral plumes suspended in translucent chalcedony.