Fossiliferous Limestone with Rugose Coral
Calcium Carbonate (Calcite) var. Limestone with Rugosa fossils · Mineral Specimen / Sedimentary Rock
Crystal System
Trigonal (individual calcite crystals) in a massive sedimentary habit; fossils display radial and bilateral symmetry.
Mineral Group
Carbonates (Calcite subgroup)
Chemical Formula
CaCO3 with minor Mg, Fe, and organic matter
Formation Process
Sedimentary: Result of lithification of marine skeletal fragments and lime mud over millions of years, often in shallow warm seas.
About This Crystal
An opaque, massive sedimentary rock matrix with a dull, earthy luster and grey-to-buff coloration. It features prominent fossil inclusions of Rugose ('Horn') coral, identifiable by their wrinkled, calcified outer septa and cone-like structure.
Physical Characteristics
Color: Grey/tan; Streak: White; Cleavage: Not visible in massive form; Fracture: Uneven to sub-conchoidal; Specific Gravity: 2.3-2.7; Effervesces strongly in dilute HCl.
Optical Properties
Generally opaque; individual calcite crystals within may show double refraction and vitreous luster under magnification.
Hardness & Durability
Origin Region
Global; common in Paleozoic limestone beds of North America (e.g., Midwest) and Europe (e.g., Britain).
Hardness & Durability
Mohs Hardness: 3; brittle and easily scratched by steel; low durability for jewelry but excellent for educational specimens.
Care & Maintenance
Avoid all acids (vinegar, etc.); clean only with warm water and mild soap; handle gently to avoid chipping fossil protrusions; keep dry to prevent weathering.
Rarity & Value
Very common; low monetary value but high educational and historical value. Value increases with fossil preservation quality and matrix stability.
Special Characteristics
Features macro-fossils (Rugose coral); often exhibits pale yellow fluorescence under UV light due to organic content within the limestone.
Lore & History
Historically used as a construction material and in lime production. Symbolically associated with grounding and the passage of time. Rugose corals are an extinct order of coral that vanished during the Permian–Triassic extinction event.