What is a stromatolite in geology ?
Stromatolite : definition
Stromatolites (or stromatolithes) are fossil carbonate constructions. These concentric cauliflower-like structures are usually formed in shallow waters by colonies of photosynthetic cyanobacteria ("blue algae"), which still exist today. They are among the oldest known fossils, and certainly the oldest macrofossils ; they have been known for 3.5 billion years in Australia. In France, the basin of Limagne around Clermont-Ferrand constitutes the 3rd world deposit of stromatolites, whole banks are observable with the outcrop in many places like with the quarry of Gandaillat. The photo on the right shows a stromatolite formation with a load figure in the sediments of La Mine des Rois de Dallet (Puy-de-Dôme). Stromatolites are now widely used in jewelry and ornamentation.
Stromatolite cabochon from Peru
Stromatolite cabochon from Peru
Stromatolites from Sharkbay, Australia - © Paul Harrison