Limestone (Micritic)
Sedimentary Rock (Calcium Carbonate var. Limestone) · Mineral Specimen / Sedimentary Rock
Crystal System
Trigonal (as constituent Calcite), but specimen habit is Massive/Rock-form
Mineral Group
Carbonates (Calcite group)
Chemical Formula
CaCO3 (with possible Mg, SiO2, or Fe impurities)
Formation Process
Sedimentary: Biogenic or chemical precipitation of calcium carbonate in marine environments, followed by lithification.
About This Crystal
A fine-grained, massive grey rock with a dull, earthy luster. It is opaque, displaying a weathered, pitted surface typical of chemical erosion by acidic rainwater.
Physical Characteristics
Grey body color, white streak, no visible cleavage in massive form, sub-conchoidal to uneven fracture, specific gravity 2.5-2.7, non-magnetic, effervesces in HCl.
Optical Properties
Generally opaque in hand specimen; individual calcite components are doubly refractive with high birefringence (usually only visible under a microscope).
Hardness & Durability
Origin Region
Global distribution; common in the UK, USA, and Southern Europe. Forms in marine environments.
Hardness & Durability
Mohs hardness 3 (Calcite-based). Brittle tenacity, low durability for jewelry, sensitive to acids and abrasive wear.
Care & Maintenance
Avoid acidic cleaners (vinegar, lemon juice). Clean with water and soft cloth. Store away from harder stones to prevent scratching.
Rarity & Value
Common. Minimal monetary value as a single specimen; value factors include presence of fossils or specific decorative patterns.
Special Characteristics
Strong effervescence when exposed to weak acid; may contain micro-fossils or show pitting from chemical weathering (karstification).
Lore & History
Historically used as a primary building material (Pyramids of Giza). Metaphysically associated with grounding and centering properties.