Iraqi National Journal of Earth Sciences

Abstract

The petrography and mineralogy of two types of technical plaster, an English dental stone and two types of local juss were studied.
Thee petrography of the studied thin sections, revealed that technical plasters consist of dispersed prismatic, monoclinic crystals, with ill – defined edges ( bassanite of the β –hemihydrate). Dental stone consists of more packed, prismatic monoclinic crystals with well defined and sharp edges (bassanite of the α – hemihydrate ). Some crystals are pseudo- hexagonal. Bassanite of local juss in thin sections is identical to that of technical plasters.
x-ray diffraction studies proved that technical plaster consist of about (95%) bassanite and (5%) gypsum, compared with (99%) bassanite and (1%) gypsum for the English dental stone. Local juss consists of anhydrite (63-70%), bassanite (20%) and gypsum (10-17%).
The three mineral phases, in the final product, the juss, exist as a mechanical mixture, rather than transformation phases. The occurrence of a phase is a function of the distance of raw material, the gypsum from fire source.