Rock & Mineral Encyclopedia

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

Coober Pedy Opal

Australia's classic light-bodied precious opal from Coober Pedy, famed for milky white stones flashing pastel rainbow play-of-color.

An opaque blue variety of chalcedony jasper, less common than red or green forms, colored by mineral inclusions.

The most common precious opal, with a pale milky body that shows softer pastel flashes of play-of-color throughout.

A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.

Ilmenite is the world's leading source of titanium, a heavy iron-black oxide common in mafic rocks and black sands.

A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.

A bronze-colored iron sulfide notable for being the most magnetic of the common sulfide minerals and an important nickel host.

The most common variety of quartz, milky white from microscopic fluid and gas inclusions, forming massive veins worldwide.

An ultramafic rock of olivine and clinopyroxene, a peridotite variety common as cumulate layers in mafic intrusions.

The sodium end-member of the plagioclase feldspar series, a common white rock-forming mineral and parent of peristerite moonstone.

Goethite is a common brown iron oxyhydroxide, the main crystalline component of limonite and rust, with shimmering botryoidal forms.

The most common type of mantle peridotite, made of olivine with both orthopyroxene and clinopyroxene, representing fertile upper-mantle rock.

The calcium end-member of the plagioclase feldspar series, a high-temperature mineral common in mafic rocks, meteorites and lunar samples.