sedimentary

Fossiliferous Limestone

Biogenic Limestone (Calcium Carbonate, CaCO3)

Hardness: 3 (Mohs scale); Color: Dark grey to charcoal with white/tan biological inclusions; Luster: Dull/Earthy; Structure: Massive with micro-fossil fragments; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Color: Dark grey to charcoal with white/tan biological inclusions
Luster: Dull/Earthy

Identified April 20, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in warm, shallow marine environments through the accumulation of organic debris, such as shell fragments and corals, which are later lithified. Most often dates from the Paleozoic or Mesozoic eras.

Uses & applications

Primary source of lime for cement, used in construction (crushed stone), soil conditioner in agriculture, and as a decorative building stone.

Geological facts

This specific piece appears to contain 'hash' or fragments of ancient marine life, possibly crinoid stems or small bivalve fragments. Limestone preserves the history of Earth's ancient oceans and represents one of the largest carbon sinks on the planet.

Field identification & locations

Identify in the field by its reaction (fizzing) when exposed to a drop of dilute hydrochloric acid (vinegar may work weakly). Look for visible shell fragments or small tubular shapes on weathered surfaces. Commonly found in former seabed regions.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary