What is the difference between high Mg and low Mg calcite?

Question

What is the difference between high Mg and low Mg calcite?

Answer 1

low mg calcite is formed from coralline algae, whereas high mg calcite is called calcite and is formed in anaerobic conditions in supersaturated saline lagoons

Answer 2

I really have no idea

Answer 3

Calcite is Ca + CO3 - you can get minor amounts of  Magnesium substituting for Calcium, the amount of magnesium substituting would result in high or low Mg calcite (you can also have Fe, Zn, Mn substitution).  Dolomite is (Ca, Mg) (CO3)2 - essentially equal amounts of calcium and magnesium.

One of the interests in magnesium content of calcite is in the investigation of oceanic fossils.