Rock & Mineral Encyclopedia

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

Reedmergnerite

A rare boron-bearing feldspar, the boron analogue of albite, first found in oil-shale nodules of the Green River Formation.

Agate that forms in flat cracks or veins of host rock rather than rounded nodules, producing straight, parallel banding.

An opaque grey-brown common opal forming nodules and concretions, historically called liver opal for its dull brownish color.

A lightweight black organic gemstone formed from fossilized wood under pressure, a type of lignite long used in mourning jewelry.

A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.

A rare black carbon-rich rock from Russia, noted for containing fullerenes and ranging from dull mineralized stone to lustrous noble shungite.

Syrian Garnet is an old trade name for fine deep-red almandine, historically tied to the Syriam region and prized as 'precious garnet.'

A durable magnesium aluminum oxide gem that occurs in many colors and was long mistaken for ruby.

A common rock-forming potassium feldspar, the Mohs hardness reference at 6, found in granites and used in ceramics and glassmaking.

A group of green magnesium silicate minerals with a smooth, waxy feel, often carved and sometimes sold as imitation jade.

The classic gem opal that flashes shifting spectral colors, defined by the diffraction effect known as play-of-color.

The rarest and most valuable opal, with a dark body tone that makes its flashing rainbow play-of-color blaze brilliantly.

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

Opal from Australia, the world's leading source of precious opal, ranging from white and crystal to prized black and boulder types.