Calcite

Calcite is the defining mineral of limestone and marble, the foundation of coral reefs, and a major component of most sea shells and cave formations. It is also one of the most diverse collector minerals on the planet — forming in more than 300 documented crystal habits and occurring in a spectacular range of colors, localities, and associations.

Properties

Crystal Habits

Calcite grows in an astounding variety of forms:

• Rhombohedra – Has six faces that are all rhombuses
• Scalenohedral (dogtooth calcite) – Tall, pointed crystals in stellar clusters
• Nailhead calcite – Flat-topped crystals with a distinct disc shape
• Iceland spar – Large, perfectly cleaved colorless rhombs (a rhombohedral habit) displaying remarkable double refraction
• Stalactites and stalagmites – Cave formations composed almost entirely of calcite
• Manganocalcite – Pink to rose calcite colored by manganese impurities

Where It's Found

Calcite is found globally, but notable localities include:

• Chihuahua, Mexico – Produces excellent golden and orange scalenohedral crystals and beautiful manganocalcite.
• Tsumeb, Namibia – A legendary polymetallic deposit that has yielded extraordinary calcite crystals in association with rare secondary minerals.
• England (Peak District, Yorkshire) – Classic dogtooth and twinned calcite in lead-mine gangue material.
• Iceland – Source of "Iceland spar," large, optically clear calcite crystals historically used in Nicol prisms.
• Tennessee and Missouri, USA – Mississippi Valley-type lead-zinc districts produce excellent calcite crystals, often associated with sphalerite and galena.
• Peru – Pink manganocalcite and colorful cobaltocalcite are highlights of Peruvian mineral production.

Special Properties

Double Refraction (Birefringence): Clear calcite crystals placed over text will show two images — a striking demonstration of the mineral's strong birefringence. This property made Iceland spar historically important in the development of polarized light optics.

Reaction to Acid: Calcite fizzes vigorously in dilute hydrochloric acid, producing CO₂. This is the definitive field test for calcite versus other carbonates.

Fluorescence: Many calcites fluoresce — some brilliantly — in pink, orange, red, or blue under UV light.

Collecting Tips

• Crystal habit diversity. Collecting calcite by crystal form is a rewarding specialty within mineralogy. No two habits look alike.
• Association specimens. Calcite often grows with galena, sphalerite, pyrite, or fluorite. Combination specimens can be very attractive.
• Test for acid reaction. If you are uncertain whether a white carbonate mineral is calcite or another species, a drop of dilute HCl tells the story quickly.
• Softness. Mohs 3 means calcite scratches easily. Keep specimens isolated in storage.

Care & Storage

At Mohs 3, calcite is easily scratched. Keep it padded and separated from harder minerals. Never clean with acid — even mild acids will etch or dissolve the surface. Use only a soft dry brush or damp cloth. Avoid prolonged humidity, which can promote surface deterioration.

Browse Calcite Specimens

Mineral Kingdom stocks calcite specimens from a variety of localities and habits. View available calcite listings in our shop to find a form or color that completes your collection.