No discussion of carbonate origin is complete without addressing [CaMg(CO₃)₂]. The classical problem: Dolomite is abundant in ancient rocks (Precambrian to Paleozoic) but extraordinarily rare in Holocene sediments.
: Most carbonates form from the skeletal remains of marine organisms like corals, mollusks, and algae. In tropical "photozoan" factories, light-dependent organisms precipitate calcium carbonate ( CaCO3cap C a cap C cap O sub 3 ) to build reefs and shells.
The classic "problem" – abundant ancient dolomite, rare modern dolomite – is partially resolved via:
New research suggests that is the missing link. Specific sulfate-reducing bacteria lower the energy barrier for magnesium to incorporate into the crystal lattice, allowing dolomite to form at low temperatures. This "microbial model" is now the leading theory for the origin of massive Precambrian and Paleozoic dolostones. 4. Carbonates and the Global Carbon Cycle
