sedimentary

Stromatolite

Biogenic sedimentary rock (Calcium carbonate / Dolomite)

Hardness 3-4 on Mohs scale, typically gray, brown, or black, dull to earthy luster, layered micro-structure formed by microbial mats.

Identified October 24, 2026More sedimentary →

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Physical properties

Hardness 3-4 on Mohs scale, typically gray, brown, or black, dull to earthy luster, layered micro-structure formed by microbial mats.

Formed through the trapping and binding of sediment by colonies of micro-organisms, primarily cyanobacteria, dating back billions of years.

Used primarily in scientific research to study early Earth history and ancient atmospheres, and as collectible geological specimens.

Stromatolites are Earth's oldest known fossils and played a crucial role in producing oxygen in the early atmosphere through photosynthesis.

Identified by distinctive concentric or wavy internal lamination layers; found globally in ancient marine and lacustrine limestone deposits.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)