Mineralogy, Geochemistry and Genesis of Middle Riphean Phosphatic Carbonates, Tirohan Limestone (Lower Vindhyan Supergroup), Chitrakut Area, Central India

In the Tirohan Limestone (Formation), collophane is associated with stromatolite-bearing horizon near Janaki Kund, Chitrakut area, Madhya Pradesh. It occurs as pellets, stromatolite laminae and as an envelope around stromatolites. The collophane is identified as carbonate fluorapatite which is confirmed by cell dimensions with a (Å) = 9.3638 and c (Å)= 6.8934. The C0₂ content is 1.80%, δ¹³C (organic), value for collophane is -21.99 PDB. The apatite does not show any correlation with any major or minor elements except with Ca with which it has poor positive correlation. It is envisaged that the apatite must have been formed on the stromatolite surfaces below sedirnent/water interface by the activity of microorganisms dominated by sessile bacteria.