Limestone
Sedimentary Calcite var. Limestone · Decorative Stone / Industrial Mineral / Sedimentary Rock
Crystal System
Trigonal (microcrystalline); habit is massive, fine-grained, and non-crystalline in appearance
Mineral Group
Carbonates (Calcite group)
Chemical Formula
CaCO3 (Calcium Carbonate) with possible impurities of SiO2, Al2O3, and Fe2O3
Formation Process
Sedimentary. Forms through the accumulation of shell, coral, algal, and fecal debris, or via chemical precipitation of calcium carbonate from lake or ocean water.
About This Crystal
A dense, massive gray specimen with a fine-grained, microcrystalline texture. It is opaque with a dull to earthy luster and uneven surface topography showing weathering pits and rounded edges.
Physical Characteristics
Color: Light to medium gray; Streak: White; Cleavage: None (in massive form); Fracture: Uneven to sub-conchoidal; Specific Gravity: 2.3–2.7; Fluorescence: May show weak orange or pink under UV light; Effervesces in dilute HCl.
Optical Properties
Generally opaque in hand specimen; individual calcite grains are doubly refractive but too small to see; Refractive Index: 1.486–1.658; No pleochroism visible in massive form.
Hardness & Durability
Origin Region
Found globally; major deposits in the United Kingdom (Portland), USA (Indiana), France, and Egypt. Formed in shallow marine environments.
Hardness & Durability
Mohs Hardness: 3; Toughness: Poor (brittle); Stability: Sensitive to acids and soft enough to be scratched by steel; low wearability for jewelry.
Care & Maintenance
Avoid all acids (including vinegar and citrus); clean only with pH-neutral soapy water and a soft cloth; store away from harder stones like quartz to prevent scratching.
Rarity & Value
Very Common; low monetary value as a mineral specimen; value is based on industrial use or architectural utility; rarely treated unless stabilized for masonry.
Special Characteristics
Strong effervescence when in contact with hydrochloric acid; frequently contains fossilized remains of marine organisms, though none are sharply defined in this view.
Lore & History
Historically used as the primary building material for the Great Pyramids of Giza and Roman colosseums; symbolically associated with grounding and ancestral wisdom in traditional lore.