Calcite Geode (with Calcedony rim)
Calcite (Calcium Carbonate) · Mineral Specimen / Geode
Crystal System
Trigonal; typically occurring in rhombohedral crystals, or in this case, a massive/microcrystalline habit filling a vug.
Mineral Group
Carbonates (Calcite Group)
Chemical Formula
CaCO3
Formation Process
Secondary mineralization through hydrothermal or sedimentary precipitation; calcium-rich groundwater fills cavities in host rock.
About This Crystal
The specimen features a tan to light-brown crystalline center with a vitreous to pearly luster. It is surrounded by a white, opaque to translucent outer rim of chalcedony or microcrystalline calcite, embedded in a darker host matrix.
Physical Characteristics
Color: Tan/Brown center, white rim; Streak: White; Cleavage: Perfect rhombohedral (not visible in this massive form); Specific Gravity: 2.71; Fluorescence: Often exhibits strong orange, red, or blue under UV light.
Optical Properties
Refractive Index: 1.486 - 1.658; Birefringence: Extremely high (0.172); typically transparent to translucent with a vitreous luster.
Hardness & Durability
Origin Region
Commonly found in sedimentary limestone regions such as Morocco, Mexico, or the Midwestern USA (Keokuk region).
Hardness & Durability
Mohs Hardness: 3; very soft and easily scratched by copper or steel. Brittle tenacity makes it susceptible to impact damage.
Care & Maintenance
Avoid all acids (even vinegar), as calcite effervesces and dissolves. Clean only with warm soapy water. Store away from harder minerals like quartz to prevent scratches.
Rarity & Value
Very common; low commercial value unless exhibiting rare crystal habits or exceptional color. Often sold as affordable decorative specimens.
Special Characteristics
Displays strong double refraction (Iceland Spar property) and common fluorescence. This specimen shows a distinctive geode vug-filling structure.
Lore & History
Used historically as lime for mortar and cement. Metaphysically associated with the Sacral and Solar Plexus chakras, believed by some to be a cleanser of energy and an amplifier of learning abilities.