Rock & Mineral Encyclopedia

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

Goldstone

A man-made glittering glass packed with tiny copper crystals, traditionally reddish-brown but also made in blue and green.

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

A porous opal, typified by Ethiopian Welo, that absorbs water and temporarily becomes more transparent or changes appearance until it dries.

Precious opal with a transparent or translucent body, letting play-of-color glow with exceptional depth and clarity.

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.

Tourmaline crystals displaying two or more distinct colors at once, including the famous pink-and-green watermelon variety.

A soft, dark, organic-rich mud deposited in stagnant, oxygen-poor water, a key precursor to oil and gas source rocks.

Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.

The classic deep-red garnet — usually almandine or pyrope — long worn as the fiery 'carbuncle' gem and January's birthstone.

A soft, spongy accumulation of partly decayed plant matter that forms in waterlogged bogs and is the first step toward coal.

A water-bearing massive grossular garnet, usually green or pink, widely used as a tough jade-like carving stone.

A soft sedimentary evaporite made of massive gypsum, deposited when sulfate-rich seawater or lake water evaporates and concentrates.

A tourmaline displaying two or more distinct colors in a single crystal, prized for natural color zoning like watermelon and bicolor stones.