sedimentary

Limestone (River Pebble)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs); Color: Grey, buff, or tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (in clastic form); Specific Gravity: 2.3-2.7

Hardness: 3-4 (Mohs)
Color: Grey, buff, or tan
Luster: Dull/Earthy

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Grey, buff, or tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (in clastic form); Specific Gravity: 2.3-2.7

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. This specimen has been rounded and smoothed by fluvial or lacustrine erosion (water movement).

Uses & applications

Primarily used in construction (aggregate), cement manufacturing, and as a soil conditioner in agriculture. Decorative pebbles are used in landscaping.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary source of lime used in making glass.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and positive reaction (fizzing) to diluted hydrochloric acid. Common in riverbeds and ancient seafloors.