Calcite

What calcite is

Calcite is the most stable form of calcium carbonate and one of the most common minerals on Earth, the main component of limestone and marble. It defines hardness 3 on the Mohs scale, fizzes in dilute acid, and comes in more crystal shapes than almost any other mineral: rhombohedra, pointed scalenohedra (dogtooth), prisms, stalactites and botryoidal crusts.

Clear calcite shows strong double refraction: look through a transparent rhomb and every line appears twice. Many calcites also fluoresce under ultraviolet light, red, blue or yellow, and some keep glowing after the lamp is off.

Calcite from Morocco

Moroccan calcite is sold in many forms. The most sought after is cobaltoan calcite from the Bou Azzer cobalt district in the Anti-Atlas, where traces of cobalt colour the crystals pink to magenta; it grows alongside erythrite and skutterudite. Golden and white calcite crystals are also listed from Tounfite in the High Atlas, and calcite accompanies native silver at the Bouismas mine in the Bou Azzer district.

What calcite costs: price data from October 2026

Asking prices read on 28 October 2026.

How to judge and care for calcite

Value comes from colour (cobaltoan pink above all), sharp undamaged crystals, lustre and contrast with the matrix.

• Calcite is soft (3) and cleaves easily in three directions: protect edges.
• Never use vinegar, lemon or any acid: calcite dissolves and loses its lustre.
• Rinse in plain lukewarm water if needed and dry; avoid sudden temperature changes.
• Cobaltoan calcite from Bou Azzer grows with arsenic minerals: wash your hands after handling it.

Questions collectors ask