sedimentary

Limestone with Lichen

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, white, or light gray base with orange-yellow lichen growth; Luster: Dull or earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.7.

Hardness: 3 on Mohs scale
Luster: Dull or earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. This specific specimen shows weathering and biological colonization by crustose lichen on the surface.

Uses & applications

Primarily used in construction (aggregate, cement, building stone), chemical feedstock for lime, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. The orange spots on this specimen are actually lichen, a symbiotic organism of algae and fungi, which slowly breaks down the rock through chemical weathering.

Field identification & locations

Identify in the field by testing with a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is found globally in areas that were once ancient seabeds.

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