sedimentary

Limestone Pebble

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: White to light gray; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in hand specimen); Specific Gravity: 2.71

Hardness: 3 (Mohs scale)
Color: White to light gray
Luster: Dull/Earthy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from 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 (fluvial or coastal action). Geological ages range from Precambrian to Holocene.

Uses & applications

Used primarily in the production of cement, crushed stone for road base, architectural stone, and as a soil conditioner in agriculture. Pure white varieties are ground for use as fillers in paper, paint, and plastics.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, resulting in the formation of massive cave systems like Mammoth Cave in the USA.

Field identification & locations

Identify in the field by its light color, smooth texture when water-worn, and a positive effervescence (fizzing) reaction when touched with dilute hydrochloric acid. Commonly found in riverbeds and coastal regions near ancient seabed deposits.