INFRARED SPECTROSCOPIC STUDIES ON NATURAL LI-FE-AL-MICAS

Different chemical compositions of Li-Fe-micas and Li-phengites cause differences in some bands of the infrared spectra. This dependence was investigated in detail and applied to the detection of different mica types in a series of mixed crystals (lepidomelane-lepidolite, Li-phen gite). The samples were collected from granitoides and greisen of the Sn-W-deposit Ehrenfriedersdorf (Erzgebirge/Saxony) and the Zanchivlan granitic complex (Central Mongolia). An increasing Li-content of the L i-Fe-micas influences not only the Si-O-Li-band but also the band in t he range of 515-540 cm-1, for which a Si-O-(Al(VI), Li)-vibration shou ld be responsible. A strong relation obviously exists between the wave number of the absorption maximum in the Si-O-stretching region and th e mass of the octahedral cations. The three bands described allow the differentiation of individual members of the group of Li-Fe-micas. Fur thermore, some bands in the OH-stretching region can be used for diffe rentiation: Li-phengite - 3600 cm-1; siderophyllite, protolithionite, zinnwaldite - 3650-3660 cm-1 and 3600 cm-1; lepidolithe - 3620 cm-1 an d 3650 cm-1.