Carbonates · Sourced PROFILE
Calcite
CaCO₃
A widespread carbonate mineral and the principal component of limestone and marble.
AT A GLANCE
- Formula
- CaCO₃
- Crystal system
- Trigonal
- Space group
- R̅3c
- Mohs hardness
- 3
- Density
- 2.7102 g/cm³
- Optical character
- Uniaxial (−), with extremely strong birefringence
CRYSTALLOGRAPHY
Crystal form & structure
Rhombohedra and scalenohedra are classic, but calcite is exceptionally diverse: more than a thousand crystal forms and many twinned habits are known.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- Perfect rhombohedral cleavage on {10̅11}
- Fracture
- Conchoidal when cleavage is not expressed
- Tenacity
- Brittle
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent to opaque
- Observed colours
- Colourless or white, with grey, yellow, red, pink, green, blue, brown, or black varieties
LIGHT & OPTICS
Optical properties
- Optical class
- Uniaxial (−), with extremely strong birefringence
- Refractive index
- ω 1.658; ε 1.486
- Fluorescence & electrical behaviour
- Common and highly variable: red, orange, pink, blue, or other responses may occur under UV.
GEOLOGICAL SETTING
Formation
Forms in sedimentary, biological, hydrothermal, and metamorphic environments.
MINERAL COMPANY
Common associations
Dolomite, quartz, fluorite, barite, sulfides, zeolites, clay minerals, and many sedimentary or hydrothermal minerals
FIELD NOTES
How to identify it
Hardness 3 allows scratching with a copper coin; dilute hydrochloric acid produces vigorous effervescence. Clear cleavage fragments show obvious double refraction.
NAME & HISTORY
Where the name comes from
From Latin calx, meaning lime.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Calcite
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Dara-i-Pioz alkaline massif · Calcite is documented in carbonatite and hydrothermal-metasomatic assemblages of this unusual alkaline massif.
Sourced · ApproximateLocality precisionTrace Elements in Calcite from the Darai Piez Alkaline MassifSnezhnoe ruby and sapphire deposit, Kukurt district, Eastern Pamir · Calcite forms the marble host of the Snezhnoe ruby and sapphire deposit within the broader Kukurt district and accompanies corundum in the documented mineral assemblage.
Sourced · Region precisionRubies and Sapphires from Snezhnoe, Tajikistan (Sorokina et al., 2015)