Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Flint

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

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

A soft, pastel minty-green tourmaline prized for its fresh, light color, a delicate variety of green elbaite.

Black volcanic glass dotted with small light-colored mineral specks resembling stars scattered across a night sky.

Black volcanic glass with a warm bronze or coppery sheen produced by light reflecting off aligned microscopic inclusions.

A rare color-change chrysoberyl that appears green in daylight and red under incandescent light, sometimes called emerald by day, ruby by night.

A transparent, optical-grade variety of calcite famous for strong double refraction, splitting images and light into two rays.

A moonstone variety displaying a moving band of light (chatoyancy) across its surface in addition to the classic moonstone glow.

A warm peach-to-apricot variety of moonstone feldspar showing a soft billowy sheen (adularescence) caused by internal light scattering.

A translucent, soft blue variety of microcrystalline quartz whose color comes from light scattering through its fine structure.

The red to raspberry-pink variety of tourmaline, prized for its vivid ruby-like color that holds under both daylight and artificial light.

A lightweight black organic gemstone formed from fossilized wood under pressure, a type of lignite long used in mourning jewelry.