ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 28, (4) 289 - 309 (1984)


Part II. Classification and X-ray identification

Weiss Zdeněk 1, Ďurovič Slavomil 2
1 Coal Research Institute, 716 07 Ostrava-Radvanice
2 Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 5, 842 36 Bratislava

The MDO polytypes of pyrophyllite and talc family have been classified according to their superposition structures into two subfamilies, and accor­ding to the Y Z projection of their structures into 7 (talc family) and 15 (pyrophyllite family) MDO groups. This geometrical classification which is closely related to the diffraction patterns of these minerals, has been confirmed by systematic calculation of X-ray diffraction patterns for all individual MDO polytypes. These calculations made it also possible to construct identi­fication diagrams for determining the subfamily and the MDO group from the distribution of intensities along the reciprocal rows ±20l or ±13l and 02l, respectively. These two characteristics suffice for the determination of any MDO polytype. The identification is based on visual comparison of single-crystal diffraction patterns with the identification diagrams. A partial identification is possible also using powder diagrams of specimens with random orientation of particles.

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