Calcite
Calcite · Mineral Specimen / Common Mineral
Crystal System
Trigonal - Hexagonal Scalenohedral; Habit can be rhombohedral, scalenohedral, prismatic, or massive.
Mineral Group
Carbonates
Chemical Formula
CaCO3
Formation Process
Primarily Sedimentary (precipitation from solution) or Metamorphic (marble formation); also occurs in hydrothermal veins.
About This Crystal
The specimen shows a rough, greyish-white host rock with a vug or cavity containing white to colorless crystalline Calcite. The luster is vitreous on crystal faces to earthy on the matrix. Transparency ranges from opaque in the host rock to translucent in the crystal clusters. Small rhombohedral cleavage planes are visible.
Physical Characteristics
Color: White, grey, colorless; Streak: White; Cleavage: Perfect rhombohedral in three directions; Fracture: Conchoidal; Specific Gravity: 2.71; Fluorescence: Often fluoresces red or white under UV light.
Optical Properties
Refractive Index: 1.486 - 1.658; Birefringence: Extremely high (0.172), often showing double amber refraction in clear specimens.
Hardness & Durability
Origin Region
Worldwide; notable massive and crystalline deposits in Mexico, USA, Brazil, and Iceland.
Hardness & Durability
Mohs Hardness: 3; Toughness: Poor due to perfect cleavage; Stability: Reacts with dilute acids (effervescence); soft and easily scratched.
Care & Maintenance
Clean only with warm soapy water; avoid all acids, ultrasonic cleaners, and steam. Store separately to prevent scratching from harder minerals.
Rarity & Value
Very Common; Value is generally low for massive specimens, though well-formed crystals or those with unique inclusions can be collectible.
Special Characteristics
Strong acid reaction (effervescence); high birefringence; widespread fluorescence; often found as a secondary mineral in basalt or limestone cavities.
Lore & History
Historically used in construction (limestone/marble) and as 'Iceland Spar' for optical instruments. In metaphysical lore, it is associated with cleansing energy and the crown chakra.