Rock & Mineral Encyclopedia

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

Andesite

A fine-grained, intermediate volcanic rock common at subduction-zone volcanoes, between basalt and rhyolite in composition.

A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.

A conglomerate altered by heat and pressure, often with its rounded pebbles stretched and flattened into elongated lenses.

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.

Fine, golden, hair-like strands of basaltic volcanic glass spun from fluid lava droplets during eruptions, named for the Hawaiian volcano goddess.

Small, smooth, teardrop-shaped beads of basaltic volcanic glass formed from airborne lava droplets, often paired with Pele's hair.

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

Glacially deposited banded agates found along Lake Michigan beaches, small waterworn pebbles with concentric red and grey banding.

Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.

A gray-toned jasper with swirling cream, black, and brown leaf-like patterns, sometimes with druzy or agate pockets.

A soft lead-gray bismuth sulfide that is an important ore of bismuth, forming metallic needle-like and bladed crystals.

A chalcedony agate with soft, billowing cloud-like masses of gray and white suspended in a translucent body.

A mottled, multicolored obsidian blending black, brown, grey, and tan patches like a calico cat's patchwork coat.

The blue-grey relative of tiger's eye, a chatoyant quartz showing a shifting band of light like a bird of prey's eye.

A black volcanic glass threaded with delicate grey, swirling lace-like bands of flow lines that show beautifully when polished.