sedimentary
Limestone Cobble
Sedimentary Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs scale); Color: White, cream, or light grey with some surface staining; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in cobbles)
- Hardness
- 3-4 (Mohs scale)
- Color
- White, cream, or light grey with some surface staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: White, cream, or light grey with some surface staining; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in cobbles)
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. This specimen shows signs of fluvial or coastal weathering, resulting in its rounded cobble shape over geological time.
Uses & applications
Commonly used in construction as an aggregate, in the production of cement, for soil neutralization in agriculture, and as a base for road building.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains fossils of marine organisms and is the primary material found in karst landscapes and caves.
Field identification & locations
Identify in the field by its soft surface (can be scratched by a copper coin) and its effervescent reaction to dilute hydrochloric acid. Found globally in areas that were once prehistoric seafloors.
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