CRYSTALLOGRAPHY FOR GEOLOGISTS: TWENTY YEARS LATER

D.Yu. Pushcharovsky

Geology Department, Moscow State University, 119899 Moscow, Russia; e-mail: dmitp@dgeo.phys.msu.su

In 1978 G. Donnay and J.D.H.Donnay reviewed the aims and the problems of a crystallography course given to geology students [1]. In this context the experience in teaching of crystallography in Geology Department of Moscow State University in recent decades as well as of the public lectures in crystallography in the frame of the education program of ISF is discussed. The failure rate in the course is basically the same (~10% in McGill University in 1978 as compared with ~12% after 1st attempt in 1998 in Moscow State University).

Some of exciting recent developments in the field of mineralogical crystallography are considered in the course of crystallography for geologists:

i) The advantage of the use of synchrotron radiation which opens the gate to a new branch of microgeochemistry (about 20% of known minerals lack a structure determination, mainly because crystals are too small or imperfect for laboratory X-ray sources).

ii) The studies of the phase transitions of mantle minerals at high pressure and high temperature contribute to the better understanding of the composition, structure and geodynamics of the deep geospheres, based on the most recent seismotomographic data. These conclusions make a lot of additional sense for the young geologists to study the basic structural types, e.g. rutile, CaCl₂, a-PbO₂, CaF₂ predicted for possible transformations of SiO₂ in low mantle, MgSiO₃ and CaSiO₃ with perovskite-like structures, hydrous magnesium silicates as possible accumulators of water in mantle etc.

iii) The new approaches in X-ray crystallography allowed to extend the scientific ideas connected with the structural systematics of minerals, with the nature of complicate crystal chemical phenomena (microtwinning, modulation, polyhedral stacking variations etc.), with the further development of modular theory of crystals and other problems of modern structural mineralogy and crystal chemistry.

1. G.Donnay & J.D.H.Donnay: Amer. Mineral., 82 (1998), 840-846.