Rock Identifier
Fossiliferous Limestone containing a Brachiopod or Mollusk Impression (Biogenic Sedimentary Rock / Fossiliferous Limestone) — sedimentary
sedimentary

Fossiliferous Limestone containing a Brachiopod or Mollusk Impression

Biogenic Sedimentary Rock / Fossiliferous Limestone

Hardness varies around 3 on the Mohs scale. Color is dark grey to brown. Luster is dull to earthy in the matrix, with a smoother, sometimes vitreous or glossy texture on the fossil impression. Composed primarily of calcium carbonate (CaCO3) along with fine-grained organic and mineral fragments packed densely with micro…

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Physical properties

Hardness varies around 3 on the Mohs scale. Color is dark grey to brown. Luster is dull to earthy in the matrix, with a smoother, sometimes vitreous or glossy texture on the fossil impression. Composed primarily of calcium carbonate (CaCO3) along with fine-grained organic and mineral fragments packed densely with micro-fossils.

Formation & geological history

Formed in shallow, marine environments where accumulation of shell fragments, skeletal debris, and calcium carbonate mud underwent lithification (compaction and cementation) over millions of years, typically during the Paleozoic or Mesozoic eras.

Uses & applications

Used primarily in educational exhibits, fossil collecting, decorative stone, and as a raw material for lime and cement production depending on purity.

Geological facts

Limestone rocks containing distinct macro-fossils or large shell impressions like the prominent one visible here are key indicators of ancient shallow seas covering parts of the continents.

Field identification & locations

Identify in the field by testing for effervescence using dilute hydrochloric acid (it will fizz) and observing visible fossil fragments or skeletal molds embedded within the rock matrix. Found globally in sedimentary strata.

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