Limestone (River Pebble)

Physical Properties

Hardness: 3 (Mohs scale); Color: light gray to off-white; Luster: dull/earthy; Texture: fine-grained and smooth due to water erosion; Cleavage: none; Specific gravity: 2.5-2.7

Formation & Geological History

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. This specific specimen has been further shaped by river or coastal erosion (abraded into a smooth pebble).

Uses & Applications

Used in construction (aggregate), cement manufacturing, soil conditioning (lime), and as a common decorative garden stone.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary source of carbon for the global cycle and often contains micro-fossils not visible to the naked eye.

Field Identification & Locations

Identify in the field by its softness (can be scratched by a steel nail) and its reaction to dilute hydrochloric acid (it will fizz/effervesce). Look for it in riverbeds or coastal areas.

Identified on: 4/21/2026

Mode: Standard