Microcrystalline Limestone Pebble

Physical Properties

Hardness: 3-4 (Mohs scale); Color: Cool gray/blue-gray with fine white speckling; Luster: Dull/Matte (earthy); Crystal structure: Traces of microcrystalline calcite; Cleavage: None (conchoidal to irregular fracture); Specific gravity: 2.3–2.7

Formation & Geological History

Formed through the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Over millions of years, pressure and chemical processes cement these sediments into solid rock. This specimen has been rounded and smoothed by high-energy water transport (river or beach erosion).

Uses & Applications

Used primarily in the construction industry as aggregate for concrete, in the production of lime and cement, and ground down for soil conditioning in agriculture.

Geological Facts

Limestone covers about 10% of the Earth's total land surface. Because it is soluble in rainwater, it is the primary rock responsible for the formation of spectacular karst landscapes, including caves and sinkholes.

Field Identification & Locations

Identify in the field by its softness (it can be scratched by a steel blade) and its reaction to weak acid (it will fizz/effervesce when exposed to vinegar or HCl). Commonly found in dry creek beds, riverbanks, and coastlines near marine deposits.

Identified on: 4/24/2026

Mode: Standard