Rock & Mineral Encyclopedia

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

Iceland Spar

A transparent, optical-grade variety of calcite famous for strong double refraction, splitting images and light into two rays.

An extremely common calcium carbonate mineral that comes in nearly every color and shows strong double refraction in clear crystals.

A soft, soothing powder-blue variety of calcite, a common calcium carbonate mineral often sold as gentle tumbled stones.

A soft, glowing orange variety of calcite colored by iron oxides, popular as tumbled stones and known for fizzing in acid.

Coarse, clear-to-white crystalline calcite that cements limestones, contrasting with fine muddy micrite.

A soft, fine-grained, translucent form of gypsum (or banded calcite) long prized as a carving and ornamental stone.

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

A soft, colorful calcium fluoride mineral famous for cubic crystals, perfect octahedral cleavage, and fluorescence under UV light.

A clear, soft crystalline variety of gypsum that forms glassy or fibrous wands, so soft it can be scratched with a fingernail.

A water-free calcium sulfate mineral closely related to gypsum, forming in evaporite deposits and swelling into gypsum when it absorbs water.

A calcium-magnesium carbonate mineral and rock similar to limestone but harder and only weakly reactive to acid.

A very soft sulfate mineral defining Mohs 2, occurring as selenite, satin spar, alabaster, and desert rose, used to make plaster.

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