A study on the relationship between the color and paramagnetic impurities in dolomite-marble

Conclusions

To sum up, the following conclusions can be reached from this work:

• 1. The analytic results for Mn²⁺ contents of the eight marble samples of different colors indicate that the color has nothing to do with Mn²⁺. Brown-black or darkred color of the three samples collected from the surface is caused mainly by high-valence Mn and contamination by oxides and hydroxides of Fe. The Fe³⁺ spectra of sample N₅ at 83 m underground indicate that Fe³⁺ did not enter the crystal lattice. Its dark-red color is basically caused by locally enriched Fe³⁺ compounds.

• 2. The approach parameters of EPR spectra for dolomite (Fu Yude et al., 1986) and dolomite-marble indicate that almost all the Mn²⁺ in dolomite-marble are at the Mgsite. This cannot be explained by the crystal — field theory. Based on ion radius and the distortion degree of ligand-polyhedron, a satisfactory explanation has been proposed (Fu Yude et al., 1986 ).

• 3. EPR technique, in conjunction with other methods, is not only an important tool for studying trace paramagnetic impurities in minerals and mineral colors, but also possesses great significance for studying the colors of rocks. The explanation of spectra, however, must be based on detailed mineralogical observation.