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 Tourmaline
The green variety of tourmaline, also called verdelite, ranging from bright grass green to deep forest tones colored by iron.
gemstone
Plum Tourmaline
A purplish, plum-toned elbaite tourmaline colored by manganese, blending the red of rubellite with violet-blue undertones.
gemstoneIce Opal
A clear, glassy, near-colorless opal resembling ice, sometimes with subtle internal flashes of play-of-color.
gemstone
White Opal
The most common precious opal, with a pale milky body that shows softer pastel flashes of play-of-color throughout.
gemstoneSard
A brownish-red to deep brown variety of chalcedony, closely related to carnelian but darker, colored by iron oxides.
mineral
Chalk
A soft, white, fine-grained limestone made almost entirely of microscopic marine plankton skeletons.
sedimentary
Sphalerite
Zinc sulfide and the chief ore of zinc, prized when transparent for its extreme fire that exceeds diamond.
mineral
Molybdenite
Molybdenite is the primary ore of molybdenum, a soft, greasy, silver-gray sulfide that closely resembles graphite.
mineral
Chromite
Chromite is the only commercial ore of chromium, a black iron-chromium oxide of the spinel group found in mafic igneous rocks.
mineral
Mica Schist
A glittery, strongly foliated rock made mostly of aligned mica flakes that split into thin, shiny sheets.
metamorphic
Harlequin Opal
The rarest and most coveted opal play-of-color pattern, showing large, evenly spaced, angular mosaic patches of color.
gemstone
Rock Salt
An evaporite rock of the mineral halite (sodium chloride), the source of common salt, with a distinctive salty taste.
sedimentary
Lodestone
A naturally magnetized variety of magnetite that attracts iron, historically used as the first magnetic compass.
mineralDiatomaceous Earth
Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.
sedimentary
Scoria
A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.
igneous
Garnierite
A vivid green hydrous nickel-magnesium silicate that is a major ore of nickel, mined from weathered ultramafic rocks.
mineralFlame Obsidian
Black volcanic glass that flashes flame-like bands of iridescent color when light strikes aligned nanoscale inclusions.
igneousBurgundy Tourmaline
A deep wine-red to maroon tourmaline colored by manganese, a rich darker-toned member of the red-pink rubellite family.
gemstone
Cat's Eye Green Tourmaline
Green tourmaline cut as a cabochon to show a sharp moving band of light (chatoyancy) caused by fine parallel inclusions.
gemstone
Honduran Opal
Precious opal from Honduras occurring in a dark volcanic matrix, where bright flecks of color flash against a natural black basalt background.
gemstoneMarl
A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.
sedimentary
Coquina
A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.
sedimentary
Calcirudite
A coarse-grained limestone built of gravel-sized carbonate clasts, the carbonate equivalent of a conglomerate or breccia.
sedimentary
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