Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Andalusite
A pleochroic aluminum silicate that flashes green and reddish-brown from different angles, with a cross-marked variety called chiastolite.
mineral
Matte Obsidian
Obsidian with a dull, non-reflective surface from natural weathering or deliberate sandblasting/etching, rather than a distinct type of volcanic glass.
igneous
Essexite
A dark, silica-undersaturated gabbroic rock containing nepheline along with plagioclase, alkali feldspar, and pyroxene, also known as nepheline monzogabbro.
igneous
Velvet Opal
Opal with a soft, velvety surface sheen rather than sharp play-of-color, prized for its gentle glow.
gemstone
Lepidolite
A soft lithium-bearing mica with a lilac to purple color and pearly, flaky sheen, an important ore of lithium.
mineral
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous
Achroite
The rare colorless variety of tourmaline, named from the Greek for 'without color' and prized by collectors.
gemstone
Sparite
Coarse, clear-to-white crystalline calcite that cements limestones, contrasting with fine muddy micrite.
sedimentary
Syenite
A coarse-grained intrusive igneous rock dominated by alkali feldspar with little or no quartz.
igneous
Red Opal
An opal with a deep red body color, often a variety of Mexican fire opal, prized for its warm, glowing intensity.
gemstone
Purple Obsidian
Purple-colored volcanic glass; genuine natural purple obsidian is rare, with much purple obsidian being manufactured colored glass.
crystal
Maxixe
A deep blue beryl with a color caused by radiation that fades in light, named after the Maxixe mine in Brazil.
gemstone
Double Flow Obsidian
Obsidian formed from two merged lava flows, producing a stone with two distinct bands of sheen or color.
igneous
Brown Tourmaline
Warm brown tourmaline, usually magnesium-rich dravite, with tones from pale champagne to deep coffee-brown.
gemstone
Snake Skin Agate
A chalcedony with a distinctive scaly, reptile-skin surface texture, typically in pale tan, pink, and gray tones.
gemstone
Leopard Opal
A patterned common opal with mottled, leopard-like spots and blotches, prized as an ornamental and cabochon stone.
gemstone
Calcilutite
A very fine-grained, mud-sized limestone formed from carbonate mud, smooth and dense with conchoidal fracture.
sedimentary
Crystal Opal
Precious opal with a transparent or translucent body, letting play-of-color glow with exceptional depth and clarity.
gemstone
Common Opal
Opal without play-of-color, valued for solid body hues; also called potch, it occurs in a wide range of colors worldwide.
gemstone
Cloud Agate
A chalcedony agate with soft, billowing cloud-like masses of gray and white suspended in a translucent body.
gemstone
Cherry Opal
A translucent red opal, closely related to Mexican fire opal, glowing with a warm cherry-red body color often free of play-of-color.
gemstone
Cathedral Quartz
Quartz with a stepped, multi-pointed structure of parallel side crystals resembling the spires of a cathedral.
crystal
Hydroandradite
A hydrous, iron-rich garnet of the hydrogarnet group in which hydroxyl groups substitute for silica within the andradite structure.
mineral
Yellow Tourmaline
Bright yellow to golden tourmaline colored by manganese, with the most vivid canary stones among the rarest tourmaline hues.
gemstone