Calcareous Limestone with Fossil Impressions
Sedimentary Carbonate Rock (predominantly Calcite) · Mineral Specimen / Sedimentary Rock
Crystal System
Trigonal (individual calcite grains); Rock habit is massive, lithified, and water-worn
Mineral Group
Carbonates
Chemical Formula
CaCO3 (Calcium Carbonate) with possible impurities of MgCO3 and SiO2
Formation Process
Sedimentary: Chemical precipitation of calcium carbonate or accumulation of shell, coral, and algal debris in marine environments
About This Crystal
An opaque, light-grey to tan sedimentary rock featuring a fine-grained, earthy to dull luster. This specimen exhibits smooth, water-rounded edges and contains distinct white impressions that suggest fossilized organic remains or crinoid fragments.
Physical Characteristics
Color: Grey/Taupe; Streak: White; Cleavage: Rhombohedral (on a microscopic scale); Fracture: Uneven/Sub-conchoidal; Specific Gravity: 2.71; Tenacity: Brittle; Effervesces strongly in dilute HCl.
Optical Properties
Opaque; Non-pleochroic; individual calcite crystals within the matrix are highly birefringent but not visible to the naked eye; lacks chatoyancy or dispersion.
Hardness & Durability
Origin Region
Found globally in marine basins; commonly sourced from the Great Lakes region, coastal areas, and ancient seafloors
Hardness & Durability
Mohs hardness: 3 (soft); easily scratched by steel tools; low durability for jewelry but fair for ornamental carving.
Care & Maintenance
Avoid acidic cleaners (lemon, vinegar) and harsh chemicals as they will dissolve the rock. Use warm soapy water and soft brushes. Store away from harder minerals like quartz.
Rarity & Value
Very Common; primarily valued as a collectible specimen or for industrial use (construction and cement). Fossiliferous varieties hold moderate interest for amateur geologists.
Special Characteristics
Contains fossilized imprints/molds; potential for dull red or orange fluorescence under UV light depending on manganese or organic content.
Lore & History
Historically used as the primary building material for the Pyramids of Giza. Metaphysically associated with the Root Chakra and believed in folk lore to aid in grounding and centering during periods of change.