sedimentary

Limestone with Lichen/Algae

Sedimentary Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Softness (Mohs 3), cream to light gray color with green surface staining, dull/earthy luster, fine-grained texture, reacts to dilute hydrochloric acid (effervescence)

Identified July 21, 2026More sedimentary →

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Physical properties

Softness (Mohs 3), cream to light gray color with green surface staining, dull/earthy luster, fine-grained texture, reacts to dilute hydrochloric acid (effervescence)

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, and algal debris over millions of years. This piece shows surface weathering and colonization by biological organisms like lichen or green algae.

Uses & applications

Primarily used as a building material, aggregate for concrete, manufacture of lime, and as architectural stone. In this raw form, it is decorative or a landscape element.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. The green spots are likely biological (algae or lichen) rather than mineral inclusions like chlorite or malachite.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and positive acid test. It is ubiquitous in regions that were underwater during the Phanerozoic eon.