Iron sulfides and magnitite were also found. These minerals are commonly produced by anaerobic bacteria and other microscopic organisms.

A) Low maginfication of Fe-rich rim containing fine grained magnetite and Fe-sulfide phases and their association with the surrounding carbonate.

B) High magnication of a magnetite-rich area in A) showing the distribution of individual magnetite crystals. C) high magnification of a pyrrhotite-rich region showing the distribution of individual pyrrhotite particles (two black arrows in the centre) together with magnetite (other arrows) within fine-grained carbonate.

Courtsey of Science on Line.