What is it?
Calcite, as the name suggests is a naturally occurring mineral calcium carbonate (CaCO3). Its composition is identical to that of limestone but the latter occurs as sedimentary beds.Calcite is present extensively in Rajasthan, India, where Anand Talc is located. It is found in veins traversing various rock types particularly within the Aravalli and Ajabgarh series, which are ancient mountain ranges of Rajasthan. Calcite veins 30 to 150 cm thick, running uniformly sometimes for long distances, are usually found. Calcite of very high brightness of upto 99% is found in Rajasthan.
Calcite structure is formed by an ionic interaction Ca2+ (calcium cation) and CO32- (carbonate anion). For every one carbonate anion there is one calcium cation, thereby making the structure electrically neutral.
A common pattern of arrangement of ions is shown below.
- Tactile properties: It is rough and abrasive.
- Visual properties:
- Color: It is white in color but is also found in various shades like pink, brown etc, depending upon the impurities present. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities.
- Luster: It’s luster is vitreous to pearly on cleavage surfaces in crystallized varieties and vitreous to resinous to dull in massive forms.
- Streak: It’s streak is white.
- Diaphaneity: It is transparent to opaque.
- Structural properties: It has a defining mohs hardness of 3, a specific gravity of 2.71
- Affinity to water: Calcite has the ability to adsorb and absorb moisture. However, it has very poor solubility in pure water. In groundwater or rainwater, it can either be dissolved or precipitated depending on several factors including the water temperature, pH, and dissolved ion concentrations. For example, ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. It exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. In any case, whether dissolved or suspended, calcite has high dispersibility in water.
- Affinity to oil: It has low oil absorption capacity.
- Heat properties:
- Thermal conductivity: 5.526 to 4.646W/(m K) at 273 K
- Specific heat capacity: 0.203 cal/(g K) at 273 K
- Thermal expansion coefficient: 25.8 x 10-6/K to -4.7 x 10-6/K
- Melting point: 1612 K: Decomposition: 850 °C
- Electric properties: It is poor conductor of electricity.
- Combustion properties: It non explosive and non-inflammable.
- Chemical properties: It dissolves in acids