sedimentary

Limestone with Lichen

Calcium Carbonate (CaCO3) with Endolithic/Epilithic Lichen

Hardness: 3-4 (Mohs); Color: White, gray, or tan matrix with green/black organic patterns; Luster: Dull to earthy; Structure: Fine-grained crystalline; Cleavage: None (conchoidal to irregular fracture).

Hardness: 3-4 (Mohs)
Color: White, gray, or tan matrix with green/black organic patterns
Luster: Dull to earthy

Identified July 12, 2026More sedimentary →

Explore Limestone with Lichen in the encyclopedia →

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 from the accumulation of shell, coral, and algal debris. The dark patterns are biological growths of lichen (symbiotic algae and fungi) that colonize the surface and micro-fissures over long periods.

Uses & applications

Primarily used in construction (aggregate, cement), agriculture (lime), and as a building stone. In this state, it is mainly a natural landscape element.

Geological facts

The intricate green/black designs are often mistaken for fossils (dendrites), but are actually living organisms that slowly weather the rock by secreting acids.

Field identification & locations

Identify by its reaction to dilute hydrochloric acid (it will fizz) and the characteristic crustose growth of the lichen. Common globally in karst landscapes and rocky outcrops.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Mudstone

Argillite / Siliciclastic sedimentary rock

sedimentary

Brown Sandstone (River Rock)

Arenite

sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary