Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Tuff
A light, porous volcanic rock formed from compacted and cemented ash erupted during explosive eruptions.
igneous
Shale
The most common sedimentary rock, a fissile mudrock of compacted clay and silt that splits into thin layers.
sedimentary
Quartzite Sandstone
A tough, quartz-rich sandstone cemented by silica, transitional toward true quartzite but still sedimentary in origin.
sedimentary
Pumpkin Obsidian
An orange-to-rust colored variety of natural volcanic glass whose warm tone comes from iron oxide staining within the obsidian.
igneous
Orange Obsidian
Obsidian colored orange by iron oxide inclusions; vivid uniform orange material is frequently manufactured glass rather than volcanic.
igneous
Leuco Garnet
The rare colorless variety of grossular garnet, a near-flawless transparent gem free of the iron and chromium that color most garnets.
gemstone
Green Marble
A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.
metamorphic
Claystone
A very fine-grained sedimentary rock made mostly of clay minerals, smooth to the touch and lacking the gritty feel of siltstone.
sedimentary
Chrysoberyl
An exceptionally hard beryllium aluminum oxide prized for golden hues, sharp cat's-eye effect, and the rare color-change alexandrite variety.
gemstone
Buddingtonite
A rare ammonium feldspar formed by hydrothermal alteration, in which ammonium ions replace potassium, and a useful exploration indicator.
mineral
Breccia
A coarse rock of angular, sharp-edged fragments cemented in a matrix, marking nearby rockfall, faulting, or impact.
sedimentary
Blue Goldstone
A man-made glittering glass colored deep blue with cobalt and studded with tiny copper crystals that mimic a starry night sky.
gemstone
Tintenbar Opal
Rare precious opal from Tintenbar in northern New South Wales, Australia, occurring in volcanic basalt rather than sedimentary rock.
gemstone
Tetrahedrite
A gray copper-antimony sulfosalt of the fahlore group, an important ore of copper and often silver, forming tetrahedral crystals.
mineral
Siltstone
A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.
sedimentary
Red Sandstone
Iron-stained sandstone whose red color comes from hematite coatings, formed in oxidizing desert, river, and coastal environments.
sedimentary
Peach Moonstone
A warm peach-to-apricot variety of moonstone feldspar showing a soft billowy sheen (adularescence) caused by internal light scattering.
gemstone
Metabasalt
Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.
metamorphic
Lujavrite
A dark, layered agpaitic nepheline syenite rich in sodic pyroxene and amphibole with eudialyte, from the Lovozero and Ilimaussaq complexes.
igneous
Limburgite
A dark, glass-rich volcanic rock of olivine and augite phenocrysts set in a feldspar-free glassy groundmass, named from the Kaiserstuhl region.
igneous
Kyanite Schist
A mica schist containing bladed blue kyanite crystals, a marker of medium- to high-grade metamorphism of aluminous rocks.
metamorphic
Jade
A tough, prized ornamental gem that is actually two distinct minerals, jadeite and nephrite, revered for millennia in many cultures.
gemstone
Feather Jasper
A jasper marked with soft feather- or plume-like mineral inclusions that drift through a pale silica body.
mineral
Deschutes Jasper
A prized Oregon picture jasper from the Deschutes region known for soft scenic landscapes in cream, tan, and blue-gray.
mineral