We have studied a Proterozoic limestone of India and found that it is dolomite through staining. Later, we performed X-ray diffractometry and found that the dominant mineral peak is of calcite. Now, the question arises whether the staining technique is correct or the X-ray diffractometry is correct or both are correct and the reason for this discrepancy is something else.
Long time away from carbonate petrography, but regard to XRD we can be sure that both exist. Knowing that dolomite replace calcite, it is possible that the dolomite crystals are not ideally perfect dolomites. Why not examine the crystals with higher resolution techniques? particularly CL microscopy can let us know about the individual crystals
I thank both Dr. Kenneth Towe and Mr. Mohsen Kalani for their answers to my question. In fact I am more satisfied with the answer of Mr. Kalani who suggests that the dolomite has replaced calcite and the crystals have retained their relict crystal structures. Also, it is possible that the dolomite crystals are not ideally perfect dolomites.
You could also try the EPR spectroscopy provided that your sample contains Mn2+ ions, whic is almost for sure. The Mn2+ EPR spectrum is carbonates is very sensitv to local symmetry and thus could help you to identify the traces of dolomite in calcite and vice-versa.
CL or staining methods will differenciate calcite from dolomite. Be careful with the CL as dolomite may (rarely) be yellow-luminescing (just as calcite) and sometimes it is green, especially if the dolomite formed in evaporitic or hydrothermal environment.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction