sedimentary

Limestone (River Pebble)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Light gray to white with darker gray veins; Luster: Dull to earthy; Crystal structure: Hexagonal (Trigonal); Cleavage: Perfect rhombohedral in calcite form; Specific gravity: 2.71

Hardness: 3 on Mohs scale
Color: Light gray to white with darker gray veins
Luster: Dull to earthy

Identified June 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. This specific specimen has been rounded and smoothed by water erosion through river or coastal action.

Uses & applications

Used primarily in construction (cement and concrete), as a raw material for lime, in agriculture to neutralize soil acidity, and as decorative gravel.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in famous karst landscapes and cave systems like Mammoth Cave.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper coin) and its effervescence (bubbling) when in contact with a weak acid like vinegar. Found globally in areas that were once prehistoric seabeds.