sedimentary
Stromatolite
Biogenic sedimentary rock / Stromatolite
Hardness: 3-4 (due to calcite/dolomite matrix), Color: Tan, grey, brown, or banded, Luster: Dull to earthy, Crystal structure: Cryptocrystalline or microcrystalline carbonate, Cleavage: None typical for the rock as a whole
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Physical properties
Hardness: 3-4 (due to calcite/dolomite matrix), Color: Tan, grey, brown, or banded, Luster: Dull to earthy, Crystal structure: Cryptocrystalline or microcrystalline carbonate, Cleavage: None typical for the rock as a whole
Formation & geological history
Formed by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, notably cyanobacteria, in shallow marine or freshwater environments. Dating back over 3.5 billion years, they are among the oldest known fossils.
Uses & applications
Used primarily in educational displays, scientific research regarding early life on Earth, and as collector specimens.
Geological facts
Stromatolites are responsible for producing the oxygen in Earth's early atmosphere through photosynthesis, fundamentally changing the planet's chemistry and enabling complex life to evolve.
Field identification & locations
Identify by distinct layered, mounded, or columnar structures with internal laminae. Commonly found in ancient marine limestone formations worldwide, particularly Precambrian shields.
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