sedimentary
Stromatolite
Biogenic Sedimentary Rock (composed predominantly of CaCO3)
Hardness: 3-4 (Mohs scale), Color: tan, yellow, grey, and brown banding, Luster: dull to earthy, Crystal Structure: microcrystalline (biogenic layers), Cleavage: none, Specific Gravity: 2.5-2.8
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Physical properties
Hardness: 3-4 (Mohs scale), Color: tan, yellow, grey, and brown banding, Luster: dull to earthy, Crystal Structure: microcrystalline (biogenic layers), Cleavage: none, Specific Gravity: 2.5-2.8
Formation & geological history
Formed by the layering of microbial mats, specifically cyanobacteria, which trap and bind sedimentary grains. These date back billions of years (Archean to present), representing some of the oldest records of life on Earth.
Uses & applications
Used as decorative stones, in jewelry (cabochons), as educational specimens in museums, and for geological research to study early Earth environments.
Geological facts
Stromatolites provided the oxygen in Earth's atmosphere through photosynthesis. While most are fossils, living stromatolites can still be found today in places like Shark Bay, Australia.
Field identification & locations
Identified by characteristic wavy or concentric laminar patterns (calcified microbiol mats). Commonly found in ancient marine limestone formations. Collectors should look for distinct, repetitive organic banding.
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