Rock & Mineral Encyclopedia

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

Opalite

A man-made opalescent glass that glows milky blue in reflected light and warm orange when backlit, often sold as a crystal.

A rare igneous rock made mostly of carbonate minerals, source of the world's most important rare-earth-element and niobium deposits.

A man-made glittering glass packed with tiny copper crystals, traditionally reddish-brown but also made in blue and green.

A man-made glittering glass colored deep blue with cobalt and studded with tiny copper crystals that mimic a starry night sky.

A cream-colored spotted stone resembling a Dalmatian dog, made of feldspar and quartz dotted with dark mineral grains.

An intrusive igneous rock made almost entirely of plagioclase feldspar, famous as the rock of the lunar highlands.

A rare zinc oxide best known for its deep red to orange color, classically from Franklin, New Jersey, and as colorful man-made crystals.

An exceptionally coarse-grained igneous rock, often granitic, famous for hosting large crystals and many gemstones.

The most abundant mineral group in Earth's crust, feldspars are aluminosilicates that form much of granite and many igneous rocks.

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

A metamorphic rock made chiefly of manganese-rich spessartine garnet and quartz, formed from ancient manganese-bearing sediments.

A rare ultrapotassic, magnesium-rich volcanic rock from deep in the mantle, famous as the diamond host at Argyle in Australia.

A rare ultramafic volcanic rock that erupts from deep in the mantle and is the primary natural source of diamonds.

A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.

An ultramafic intrusive rock made almost entirely of olivine, representing mantle material.