A study of some manganese minerals

Abstract

On the basis of the difficulty to recognise specific manganese minerals due to their frequent mode of occurrence as fine grained aggregates the present study has been directed towards investigating properties of the minerals which might serve as a readily accessible means of identification. Towards this end attention has been focussed on X-ray diffraction patterns, micro-hardness analysis, a study of various optical properties and differential thermal analysis characteristics. X-ray diffraction patterns using Cr(Ka) radiation have been established for some twenty mineral species and provide the most satisfactory means of recognising the constituents of fine grained mineral intergrowths. The applications and limitations of micro-hardness testing are reviewed and hardness values given for the minerals studied. Attention has been paid to the variation of hardness with applied load and crystal orientation and hardness values given in selected cases. Reflectivity values for white light and for eight wavelengths within the visible spectrum are given for both air and oil. Refractive and absorption indices as determined by the method of Cambon (1949) are quoted, the latter corresponding very well with values determined by classical methods. Differential thermal analysis curves are given for the majority of the minerals, including all the more important forms, and such provide a satisfactory means of distinguishing the main mineral groups.