CALCITE

Calcite is a common and widely distributed carbonate mineral with the chemical formula CaCO₃ (calcium carbonate). It is the primary component of sedimentary rocks like limestone and marble, and the main mineral in the shells of marine organisms.

Key Properties:

Hardness: 3 on the Mohs scale (easily scratched with a knife or copper coin)
Cleavage: Perfect rhombohedral cleavage (breaks into smooth-sided blocks)
Reaction with Acid: Effervesces (fizzes) vigorously with dilute hydrochloric acid (HCl)—a key identifying feature
Transparency: Transparent to translucent
Luster: Vitreous to pearly
Color: Usually white or colorless, but impurities can produce shades of yellow, pink, blue, green, or brown

Special Optical Effect:
Calcite exhibits double refraction (birefringence)—when you place a clear calcite crystal over text, you see two images of the letters.

Uses & Applications:

Construction: Principal ingredient in cement and lime (quicklime)
Agriculture: Used to neutralize acidic soils (agricultural lime)
Industry: Flux in steelmaking, filler in paints, plastics, and paper
Decoration: Marble (metamorphosed calcite) is used in sculpture and architecture
Optics: Calcite crystals (Iceland spar) used in polarizing microscopes and optical instruments