Rock & Mineral Encyclopedia

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

Sapphire

The gem variety of corundum in every color except red, most prized in velvety blue and exceptionally hard and durable.

The red, chromium-colored variety of corundum, prized as one of the most valuable colored gemstones and second only to diamond in hardness.

The blue gem variety of corundum, prized for its rich color, extreme hardness, and brilliance second only to diamond.

A striking rock of green zoisite studded with red-pink ruby crystals and black hornblende, also called anyolite.

Montana Garnet is red almandine recovered from Montana placer gravels, often alongside the state's famous sapphires.

The hardest known natural material, a crystalline form of pure carbon prized as the ultimate gemstone for its brilliance and fire.

Natural emerald crystals still embedded in their host rock, prized as mineral specimens that show how the gem grew in place.

A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.

An earthy aluminum-rich residual rock and the world's principal ore of aluminum, often showing distinctive pea-like pisolites.