Calcite on Matrix
Calcite var. Calcium Carbonate · Mineral Specimen / Common Mineral
Crystal System
Trigonal system; typically found in rhombohedral or scalenohedral habits, though here appearing as a crystalline crust/druzy layer
Mineral Group
Carbonates (Calcite Group)
Chemical Formula
CaCO3
Formation Process
Sedimentary or Hydrothermal; forms via chemical precipitation in aqueous environments or as a secondary mineral in rock cavities.
About This Crystal
White to colorless translucent crystalline grains encrusting a dark, fine-grained host rock (matrix). Possesses a vitreous luster on crystal faces and is characterized by its rhombohedral cleavage.
Physical Characteristics
Color: White/Colorless; Streak: White; Cleavage: Perfect rhombohedral in three directions; Fracture: Conchoidal (rarely seen due to cleavage); Fluorescence: Often glows red or pink under UV light.
Optical Properties
Highly birefringent (double refraction); Refractive Index: 1.486 - 1.658; Uniaxial negative; Transparent to translucent.
Hardness & Durability
Origin Region
Global; major localities include Mexico, USA, Brazil, and China. Often found in limestone caves and hydrothermal veins.
Hardness & Durability
Mohs hardness: 3; brittle tenacity; low durability for jewelry, easily scratched by a copper coin or steel knife.
Care & Maintenance
Avoid all acids (it will effervesce and dissolve); clean only with lukewarm soapy water; store away from harder minerals like quartz to prevent scratching.
Rarity & Value
Common; value is generally low for mass-market specimens, though exceptional crystal forms or fluorescent specimens can command higher prices.
Special Characteristics
Strong double refraction (Iceland Spar variety); effervesces (bubbles) vigorously when in contact with dilute hydrochloric acid.
Lore & History
Historically used as a flux in glassmaking and as building lime. Metaphysically associated with cleansing energy and the amplification of learning and memory.