Minerals · common
Calcite
Calcite is one of the most common minerals on Earth, found in sedimentary, metamorphic, and igneous rocks. It's the primary component of limestone and marble.
Also known as: calcium carbonate, iceland spar, cave formation.
Calcite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | CaCO3 |
| Mohs hardness | 3 |
| Crystal system | trigonal |
| Luster | vitreous |
| Streak | White |
| Cleavage | Perfect rhombohedral |
| Fracture | Conchoidal |
| Specific gravity | 2.7 |
| Transparency | transparent |
| Common colors | Colorless, White, Yellow, Orange, Blue, Green, Pink |
| Rarity | common |
Geology & background
Forms through evaporation of calcium-rich water, biological processes (shells), or hydrothermal activity.
The defining mineral for 3 on the Mohs hardness scale, calcite has been studied for centuries.
How to identify Calcite
- Check whether the specimen's color and texture match typical Calcite examples.
- Photograph a fresh surface in natural light and avoid shadows, glare, or wet surfaces.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Full Calcite identification guide: checklist, home tests and look-alikes →
Calcite vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Calcite.
Where Calcite is found
Calcite is reported from multiple localities or geological settings. Exact locality should be verified from specimen provenance, maps, or field notes.
How much is Calcite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $15 |
| Premium specimen | $100+ |
Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
Common uses
- Cement production
- Optical instruments
- Collector specimens
Interesting facts
- Clear calcite (Iceland spar) shows double refraction
- Vikings may have used it as a 'sunstone' for navigation
- Forms stalactites and stalagmites in caves
Care & safety
Treat Calcite as a collector specimen unless hardness, cleavage, and fracture are confirmed.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a properly rated respirator.
Calcite FAQ
What is Calcite?
Calcite is one of the most common minerals on Earth, found in sedimentary, metamorphic, and igneous rocks. It's the primary component of limestone and marble.
How much is Calcite worth?
Entry-level Calcite specimens sell for around $2, a typical collector specimen for about $15, and premium pieces for $100 or more. Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
How hard is Calcite?
Calcite has a Mohs hardness of 3. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
Where is Calcite found?
Notable sources of Calcite include Mexico, USA, Iceland, and Brazil. Forms through evaporation of calcium-rich water, biological processes (shells), or hydrothermal activity..
What is Calcite used for?
Calcite is used for cement production, optical instruments, and collector specimens.
