A beach made of living rocks
The white shores of Lake Salda in southwestern Turkey are not sand. They are composed of hydromagnesite [Mg5(CO3)4(OH)2·4H2O], a soft carbonate mineral. This tectonic lake sits at an altitude of 1,140 meters and is one of Turkey's deepest, reaching approximately 184 meters. Its water is highly alkaline, with a pH often above 9, and high in magnesium leached from the surrounding ultramafic serpentine and dolomite rocks.
The hydromagnesite forms through a biogenic process. Microbial communities, particularly cyanobacteria, create large structures called microbialites or stromatolites. These "living rocks" precipitate the magnesium carbonate from the alkaline water, building up mounds over thousands of years. The process is slow, and the resulting structures are exceptionally fragile. Some of the mounds are massive, reaching up to 7 meters in height and coalescing into small islands. Researchers have identified diverse microbialite forms, including stromatolites, thrombolites, and dendrolites, whose structures vary with water depth and the specific microbial communities present. For example, shallow-water microbialites with abundant cyanobacteria tend to have cauliflower-like shapes, while deep-water structures with fewer cyanobacteria form finger-like columns.