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.