sedimentary
Stromatolite
Biogenic sedimentary rock / Stromatolite
Hardness: 3 to 4 (for calcitic varieties) up to 7 (if heavily silicified); Color: Tan, brown, grey, beige, or white with distinct internal layered (laminated) structures; Luster: Earthy to vitreous; Crystal Structure: Microcrystalline or cryptocrystalline (carbonate/quartz)
- Luster
- Earthy to vitreous
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Physical properties
Hardness: 3 to 4 (for calcitic varieties) up to 7 (if heavily silicified); Color: Tan, brown, grey, beige, or white with distinct internal layered (laminated) structures; Luster: Earthy to vitreous; Crystal Structure: Microcrystalline or cryptocrystalline (carbonate/quartz)
Formation & geological history
Formed by the trapping, binding, and cementation of sedimentary grains by micro-organisms, principally cyanobacteria (blue-green algae), in shallow marine or freshwater environments. Some of the oldest known fossils on Earth, dating back over 3.5 billion years.
Uses & applications
Used primarily as educational specimens, decorative display pieces, lapidary work, and by fossil collectors.
Geological facts
Stromatolites are responsible for the Great Oxidation Event, having produced much of the oxygen in Earth's early atmosphere through photosynthesis.
Field identification & locations
Identified by distinct wavy or concentric layered structures resembling cabbage leaves or domes. Found worldwide in ancient carbonate-rich sedimentary formations.
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