Calcite
Calcite (Calcium Carbonate) · Mineral Specimen / Decorative Stone / Industrial Mineral
Crystal System
Trigonal system; habit is frequently rhombohedral, scalenohedral, or massive granular.
Mineral Group
Carbonates (Calcite group)
Chemical Formula
CaCO3 (with possible trace elements like Fe, Mg, or Mn affecting tint)
Formation Process
Sedimentary (chemical precipitation in marine environments), Hydrothermal (vein filling), and Metamorphic (re-crystallization of limestone into marble).
About This Crystal
The specimen displays a characteristic vitreous to pearly luster with distinct rhombohedral cleavage planes visible. It appears translucent to opaque with a warm yellowish-honey tone, likely due to iron impurities or the lighting conditions. The surface shows a stepped growth pattern or cleavage fragmentation.
Physical Characteristics
Color: Colorless, white, yellow, or honey; Streak: White; Cleavage: Perfect rhombohedral in three directions at approximately 75 and 105 degrees; Fracture: Conchoidal (rare) to uneven; Specific Gravity: 2.71; Fluorescence: Often fluoresces red, pink, or yellow under UV light.
Optical Properties
High birefringence (double refraction) is a diagnostic feature; Refractive Index: 1.486 - 1.658; Uniaxial negative; no significant dispersion; pleochroism is generally weak or absent.
Hardness & Durability
Origin Region
Globally abundant; notable sources include Mexico, USA (Tennessee, Missouri), China, and Iceland (Iceland Spar). Found in limestone, marble, and hydrothermal veins.
Hardness & Durability
Mohs Hardness: 3 (soft); Toughness: Poor due to perfect cleavage; Low durability for jewelry, essentially restricted to earrings or pendants that won't suffer impact.
Care & Maintenance
Avoid all acids (even vinegar/lemon juice) as it will effervesce and dissolve. Clean with warm soapy water only. Store separately from harder minerals like quartz to avoid scratches. Extremely sensitive to ultrasonic cleaners.
Rarity & Value
Common; Value is generally low for massive or common rhombohedral specimens, but increases significantly for optical-grade 'Iceland Spar' or rare scalenohedral 'Dogtooth' habits.
Special Characteristics
Strongly effervesces (bubbles) in contact with dilute hydrochloric acid. Exhibits double refraction where an image viewed through a clear crystal appears doubled.
Lore & History
Historically used in building materials (lime) and optics (polarizing prisms). Traditionally associated with the Solar Plexus chakra, it is believed by practitioners to be a 'cleanser' of energy and an amplifier of learning, though these are cultural beliefs rather than scientific facts.