Rock & Mineral Encyclopedia

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

Anthracite

The highest-rank coal, a hard, lustrous black rock that burns cleanly with little smoke and high heat output.

Molybdenite is the primary ore of molybdenum, a soft, greasy, silver-gray sulfide that closely resembles graphite.

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

A plagioclase feldspar famous for labradorescence, a dramatic flash of iridescent blue, green, and gold across a dark gray stone.

A purple-toned banded chalcedony, sometimes naturally amethystine but frequently produced by dyeing gray agate.

A black volcanic glass speckled with gray-white cristobalite snowflakes, formed as obsidian begins to crystallize.

A chalcedony with a distinctive scaly, reptile-skin surface texture, typically in pale tan, pink, and gray tones.

Natural volcanic glass speckled with embedded mineral crystals (phenocrysts) such as feldspar or cristobalite that grew before the lava chilled.

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

A dark gray copper sulfide that is one of the richest copper ores, prized by collectors when found as rare sharp crystals.

Natural emerald crystals still embedded in their host rock, prized as mineral specimens that show how the gem grew in place.

The principal iron ore, a heavy iron oxide ranging from metallic silver-gray to earthy red, always leaving a tell-tale red-brown streak.

An old varietal name for alkali- and cesium-rich beryl, typically colorless to pale pink, overlapping with vorobyevite and morganite.

The calcium-aluminum garnet species spanning green tsavorite, cinnamon hessonite, and colorless leuco garnet — one of the most varied garnets.