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.

A hard, fine-grained siliceous rock with a dull porcelain-like texture, intermediate between soft diatomite and dense chert.

A hard, fine-grained siliceous rock built from the microscopic silica skeletons of radiolarians, often forming colorful ribbon-banded cherts.

A hard, dark variety of chert that knaps into razor-sharp edges and sparks against steel, central to Stone Age technology.

A black volcanic glass speckled with gray-white cristobalite snowflakes, formed as obsidian begins to crystallize.

A glowing orange-to-red opal whose warm body color resembles flame; some stones add flashes of play-of-color.

Black volcanic glass that flashes flame-like bands of iridescent color when light strikes aligned nanoscale inclusions.

A chalcedony agate with red, orange, and yellow plume or banding patterns that rise like dancing flames within the stone.

A fiery jasper whose red, orange, and yellow plumes lick across the stone like flames against an earthy background.

Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.

A glittery, strongly foliated rock made mostly of aligned mica flakes that split into thin, shiny sheets.

A bright yellow native element mineral that forms around volcanic vents and hot springs and burns with a blue flame.

A soft lithium-bearing mica with a lilac to purple color and pearly, flaky sheen, an important ore of lithium.

A rare brown chalcedony containing thin iron-oxide layers that produce flashing, fiery rainbow iridescence like trapped flames.