Rock & Mineral Encyclopedia

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

Green Marble

A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.

A soft, soothing powder-blue variety of calcite, a common calcium carbonate mineral often sold as gentle tumbled stones.

A red-toned banded chalcedony colored by iron oxides, ranging from natural carnelian-like reds to heat-treated stones.

A dense, black, mid-rank coal with high energy content, widely used for power generation and to make coke for steelmaking.

A warm golden-to-amber opal ranging from translucent common opal to precious stones that flash play-of-color over a honey body.

Precious opal from the Mintabie field in South Australia, known for hard, bright crystal opal and some dark-bodied stones.

A golden-toned opal ranging from translucent common opal to precious stones flashing color against a warm yellow body.

A glowing orange-to-red opal whose warm body color resembles flame; some stones add flashes of play-of-color.

A tourmaline displaying two or more distinct colors in a single crystal, prized for natural color zoning like watermelon and bicolor stones.

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

Quartz with a stepped, multi-pointed structure of parallel side crystals resembling the spires of a cathedral.

A limestone packed with visible shells and shell fragments, recording the accumulation of marine invertebrate remains on ancient sea floors.

A soft, spongy accumulation of partly decayed plant matter that forms in waterlogged bogs and is the first step toward coal.