Rock & Mineral Encyclopedia

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

Red Agate

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

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

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

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

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

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

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

Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.

Coarse-grained gabbro that has been metamorphosed, partly recrystallizing into amphibole, plagioclase, and other metamorphic minerals.

Rhyolite that has been metamorphosed, recrystallizing its silica-rich volcanic material into a tougher felsic metamorphic rock.

Fossil bone in which opal has replaced the original tissue, sometimes showing play-of-color, a rare collector fossil.

Fossil material whose original substance has been replaced by opal, preserving ancient shapes in common or play-of-color opal.