Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Boninite
A rare high-magnesium andesite formed in young subduction zones, named for Japan's Bonin Islands.
igneous
Fire Opal
A translucent to transparent opal in warm yellow, orange, and red tones, prized for body color rather than play-of-color.
gemstone
Pseudotachylite
A dark, glassy rock formed when frictional heat from fault movement or impact melts rock along narrow veins.
metamorphic
Holley Blue Agate
A rare translucent lavender-blue agate from the Holley area of Oregon, prized for its soft purple-blue color.
gemstonePantellerite
An iron-rich peralkaline rhyolite, a silica-rich volcanic rock named for the Italian island of Pantelleria.
igneous
Clear Tourmaline
A transparent, water-clear elbaite tourmaline (achroite), the rare colorless and highly transparent form of the tourmaline group.
gemstoneDouble Flow Obsidian
Obsidian formed from two merged lava flows, producing a stone with two distinct bands of sheen or color.
igneous
Lavender Opal
A pastel purple variety of common opal, valued for its gentle lilac body color rather than any play-of-color.
gemstoneWoodward Ranch Agate
Plume and fortification agate from the famous Woodward Ranch near Alpine, Texas, known for red and pink plumes.
gemstone
Blue Opal
A soft blue common opal, famously from Peru, valued for its serene sky-to-teal color rather than play-of-color.
gemstone
Cuprite
Cuprite is a deep red copper oxide and an important secondary copper ore, prized for its rare ruby-red gem crystals.
mineral
Spinel
A durable magnesium aluminum oxide gem that occurs in many colors and was long mistaken for ruby.
gemstone
Chlorite Schist
A soft, green, foliated rock rich in chlorite, formed by low-grade metamorphism of mafic or volcanic rocks.
metamorphic
Calcilutite
A very fine-grained, mud-sized limestone formed from carbonate mud, smooth and dense with conchoidal fracture.
sedimentary
Oolitic Limestone
Limestone built from tiny rounded ooid grains resembling fish roe, formed in warm, agitated shallow seas.
sedimentary
Tholeiitic Basalt
The most abundant basalt type on Earth, a silica-saturated subalkaline lava that forms ocean crust and flood basalts.
igneousBlue Line Jasper
A pale jasper crossed by distinctive blue-gray veins or lines, valued by lapidaries for its calm color contrast.
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
Alnöite
A rare dark ultramafic lamprophyre rich in melilite, biotite and olivine, named for Alnö Island in Sweden.
igneous
Blue Pearl Granite
A Norwegian larvikite dimension stone prized for its shimmering blue iridescent feldspar crystals.
igneous
Mustard Jasper
A warm mustard-to-ochre yellow jasper colored by iron, valued by lapidaries for its rich, earthy golden tone.
gemstoneOwyhee Blue Agate
A soft sky-blue chalcedony from the Owyhee region of Oregon and Idaho, prized for its calming, opaque powder-blue color.
gemstone
Smithsonite
Smithsonite is a zinc carbonate ore famous for glassy botryoidal crusts in blue-green, pink, and yellow hues.
mineralPaintbrush Agate
A plume agate whose inclusions form upright, bristly clusters resembling the strokes of a paintbrush.
gemstone