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

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

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

A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.

A patterned common opal with mottled, leopard-like spots and blotches, prized as an ornamental and cabochon stone.

A common opal with branching, tree-like mineral inclusions that create natural fern, moss, or landscape patterns.

A common opal containing moss- or fern-like mineral inclusions that resemble plants suspended in a pale silica body.

A common opal containing dendritic or mossy mineral inclusions that form miniature landscape-like scenes inside the stone.

An opaque, porcelain-white common opal prized for its milky, pearl-like appearance and high porosity, often carved or beaded.

An opaque to translucent milky-white common opal valued for its soft porcelain-like color rather than play-of-color.

An opal cut to show chatoyancy, a sharp moving band of light like a cat's eye, usually in honey, green or yellow common opal.