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.

A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.

A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.

A banded rhyolitic volcanic rock with swirling tan, red, and yellow iron-oxide layers prized as a decorative picture stone.

Obsidian in gray tones, often semi-translucent, colored by light scattering and minor inclusions within the volcanic glass.

A vivid yellow-and-black banded stone from Indonesian volcanic vents, colored by sulfur, arsenic minerals and iron oxides, not true jasper.

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

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

A black volcanic glass that reveals concentric rainbow bands of color when cut and polished against the light.

Black volcanic glass laced with delicate web-like veins of contrasting color, formed by flow banding and fine crystallization.

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

A rare sky-blue variety of pectolite found only in the Dominican Republic, prized for its sea-like color and white volcanic patterning.