Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Chert
A hard, fine-grained sedimentary silica rock that breaks with sharp conchoidal edges, prized by ancient toolmakers.
sedimentary
Flint
A hard, dark variety of chert that knaps into razor-sharp edges and sparks against steel, central to Stone Age technology.
sedimentary
Blue Chalcedony
A translucent, soft blue variety of microcrystalline quartz whose color comes from light scattering through its fine structure.
mineral
Porcelanite
A hard, fine-grained siliceous rock with a dull porcelain-like texture, intermediate between soft diatomite and dense chert.
sedimentary
Blue Lace Agate
A soft sky-blue banded chalcedony prized for its delicate, lace-like white and blue swirling patterns.
gemstone
Agate
A banded variety of chalcedony quartz, famed for its colorful concentric layers and enormous range of patterns and colors.
mineral
Chrysoprase
A translucent apple-green chalcedony colored by nickel, the most prized green variety of the quartz family.
gemstoneSard
A brownish-red to deep brown variety of chalcedony, closely related to carnelian but darker, colored by iron oxides.
mineral
Carnelian
A warm orange-to-red variety of chalcedony quartz colored by iron oxide, used since antiquity for seals, beads, and cabochons.
gemstone
Jasper
An opaque, often colorfully patterned variety of chalcedony quartz, popular for tumbling, carving, and jewelry.
mineral
Plume Agate
A translucent agate containing delicate three-dimensional feather- or plant-like plumes of mineral inclusions suspended in chalcedony.
gemstone
Banded Agate
The classic agate defined by concentric or parallel bands of chalcedony in varied colors, the archetype of all agate varieties.
gemstoneBlack Onyx
A solid jet-black chalcedony, usually a dyed and treated agate, prized for sleek polished beads, cabochons, and intaglios.
gemstone
Tree Agate
A white chalcedony filled with green or black dendritic, tree-like mineral inclusions that resemble ferns or moss frozen in stone.
gemstone
Fire Agate
A rare brown chalcedony containing thin iron-oxide layers that produce flashing, fiery rainbow iridescence like trapped flames.
gemstonePrase
An old name for a dull leek-green variety of quartz or chalcedony colored by green mineral inclusions, historically called mother of emerald.
crystal
Black Jasper
A dense, opaque black variety of microcrystalline quartz historically used as a touchstone for testing precious metals.
mineral
Blue Jasper
An opaque blue variety of chalcedony jasper, less common than red or green forms, colored by mineral inclusions.
mineral
Green Jasper
An opaque green variety of chalcedony quartz colored by iron and chlorite-group inclusions, prized as a durable carving and cabochon stone.
mineralFlame Obsidian
Black volcanic glass that flashes flame-like bands of iridescent color when light strikes aligned nanoscale inclusions.
igneousLace Obsidian
Black volcanic glass laced with delicate web-like veins of contrasting color, formed by flow banding and fine crystallization.
igneous
Black Agate
A deep black variety of banded chalcedony, often closely related to or treated like onyx, used for jewelry and carvings.
gemstone
Sagenite Agate
A chalcedony agate filled with radiating needle-like mineral inclusions, prized for its starburst and spray patterns.
gemstoneCloud Agate
A chalcedony agate with soft, billowing cloud-like masses of gray and white suspended in a translucent body.
gemstone