Thank you sir for this information, but then the total inorganic carbon (TIC) that we measure, doesn't it entirely come from chemically precipitated carbonates?

Yes sir, that I know. But if a carbonate shell is treated with HCl, then also CO2 will generate. My question lies there only, that how to differentiate the carbon content coming from such shells and carbonate minerals?

There is some evidence that FT-IR can discriminate between biogenic and geogenic calcites. Have you investigated this?

No, I haven't, as I didn't know about this. Thank you for the information.

The chemical precipitation is mostly calcite but biological one is mostly aragonite

I don't want to differentiate between chemically precipitated carbonates. I could not access "Lowenstam and Weiner (1989)", but read some of their other papers and it seems that by XRD and SEM analysis biologically produced carbonates can be identified. However, in samples with very low carbonate content like mine, it is not possible I guess. Nevertheless, thank you everyone for your valuable inputs.

Hello, microbial induced precipitation does not necessarily yield organic mineral compounds. Take for example Sporosarcina Pasteurii a strain which catalyses the urea hydrolysis. Hydrolysis results in the release of bicarbonate and in an increased pH in the cell's microenvironment. These conditions are favorable for the precipitation of calcium carbonate minerals under the presence of calcium. Epicellular vaterite on S. Pasteurii cells has been observed. Though this is only a metastable phase. Metastable vaterite is found to give its place to the more stable calcite phase through a transformation of the lattice of Ca2+ and CO32-ions. You can find below in the paper more details on the CaCO3 phase transition observed when applying the microbial induced calcite precipitation for soil improvement.

Article Fabric characteristics and mechanical response of bio-improv...

Thank you Dr. Towe for the information.