Rock & Mineral Encyclopedia

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

Siderite

Siderite is an iron carbonate ore, a brown rhombohedral mineral of the calcite group found in sediments and veins.

Black volcanic glass crossed by a fine network of grey or brown veins that resemble a spider's web.

A rose-pink manganese silicate marbled with black veins, prized as a tough ornamental and occasionally faceted gemstone.

Wolframite is the historic principal ore of tungsten, a heavy black tungstate forming bladed crystals in granite veins.

A white, porous borate mineral webbed with gray-black veins, widely dyed to imitate turquoise and other stones.

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

A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.

A dark, glassy rock formed when frictional heat from fault movement or impact melts rock along narrow veins.

Precious opal that forms in thin veins within brown ironstone boulders, cut with the host rock left as a natural dark backing.