Calcite
Calcite is a common and widespread mineral known for its wide variety of crystal forms and beautiful optical properties. It is composed primarily of calcium carbonate (CaCO₃) and is one of the most stable polymorphs of this compound. Calcite is found in sedimentary, metamorphic, and igneous rocks and is a major component of limestone and marble.
Chemical Composition:
Formula: CaCO₃ (Calcium Carbonate)
Crystal System:
Trigonal (rhombohedral)
Physical Properties:
Color: Usually white or colorless, but can appear in shades of gray, red, green, blue, yellow, or brown due to impurities.
Luster: Vitreous to pearly
Hardness: 3 on Mohs scale
Cleavage: Perfect in three directions (rhombohedral)
Reactivity: Effervesces (fizzes) in dilute hydrochloric acid due to the release of CO₂ gas.
Where It Occurs:
Sedimentary Environments: Most commonly in limestone and chalk, formed from marine organisms’ shells and skeletons.
Metamorphic Rocks: Found in marble, which forms from the metamorphism of limestone.
Hydrothermal Veins: Calcite can form in veins along with quartz, fluorite, and barite.
Caves: Known for forming stalactites and stalagmites through precipitation from dripping water.
Oceans and Lakes: Biogenic calcite is produced by marine organisms like coral, foraminifera, and algae.
Uses:
Used in the construction industry (cement, aggregate).
Important in agriculture (lime to neutralize soil acidity).
Optical calcite (Iceland spar) is used in optical instruments.
Used as a filler in products like paint, rubber, and plastics.
