Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Outback Jasper
An earthy Australian-style jasper in red, ochre, and yellow tones evoking the colors of the Outback desert.
mineral
Oolite
A limestone made of tiny spherical ooids, resembling fish roe, formed in warm, agitated shallow seas.
sedimentary
Molybdenite
Molybdenite is the primary ore of molybdenum, a soft, greasy, silver-gray sulfide that closely resembles graphite.
mineral
Mica Schist
A glittery, strongly foliated rock made mostly of aligned mica flakes that split into thin, shiny sheets.
metamorphic
Lodestone
A naturally magnetized variety of magnetite that attracts iron, historically used as the first magnetic compass.
mineral
Harlequin Opal
The rarest and most coveted opal play-of-color pattern, showing large, evenly spaced, angular mosaic patches of color.
gemstone
Ironstone
An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.
sedimentary
Ice Opal
A clear, glassy, near-colorless opal resembling ice, sometimes with subtle internal flashes of play-of-color.
gemstone
Gem Silica
A rare, intensely blue chalcedony colored by copper-rich chrysocolla, prized as the most valuable of the blue chalcedonies.
gemstone
Chrysoprase
A translucent apple-green chalcedony colored by nickel, the most prized green variety of the quartz family.
gemstone
Chromite
Chromite is the only commercial ore of chromium, a black iron-chromium oxide of the spinel group found in mafic igneous rocks.
mineral
Chalk
A soft, white, fine-grained limestone made almost entirely of microscopic marine plankton skeletons.
sedimentary
Black Shale
Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.
sedimentary
Basalt
A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.
igneous
Bahia Agate
A banded and plume agate from the Bahia state of Brazil, known for delicate dendritic and feathery inclusions.
gemstone
Tinguaite
A fine-grained green phonolitic dike rock rich in nepheline and aegirine, the hypabyssal equivalent of phonolite.
igneous
White Agate
A white to grayish banded chalcedony, the natural base color of much agate and the substrate for many dyed stones.
gemstone
Sapphire
The gem variety of corundum in every color except red, most prized in velvety blue and exceptionally hard and durable.
gemstone
Peacock Opal
A precious opal showing dominant peacock-like blue, green and teal play-of-color, often on Ethiopian material.
gemstone
Owyhee Blue Agate
A soft sky-blue chalcedony from the Owyhee region of Oregon and Idaho, prized for its calming, opaque powder-blue color.
gemstone
Paintbrush Agate
A plume agate whose inclusions form upright, bristly clusters resembling the strokes of a paintbrush.
gemstone
Mint Tourmaline
A soft, pastel minty-green tourmaline prized for its fresh, light color, a delicate variety of green elbaite.
gemstone
Milk Opal
An opaque to translucent milky-white common opal valued for its soft porcelain-like color rather than play-of-color.
gemstone
Merelani Mint Garnet
A delicate vanadium-colored mint-green grossular garnet from the Merelani Hills of Tanzania, the source of tanzanite.
gemstone