Beschreibung:
L'étude descriptive des roches à texture subpolyédrique s'appuie utilement sur la géométrie des modèles d'empilement. On expose ici le principe de construction des mosaïques obtenues en sectionnant des empilements de polyèdres. La méthode est appliquée aux empilements de tétrakaïdécaèdres, de rhombododécaèdres et de cube-rhombo-dodécaèdres. On compare les mosaïques modèles à quelques exemples de textures de roches, de céramiques et de métaux. Le problème de la fréquence des divers types de mosaïques données par l'empilement de tétrakaïdécaèdres est abordé. On représente enfin une répartition au hasard de deux phases puis de trois phases dispersées dans l'agrégat.
Packing polyhedra into geometric models is a useful approach to the description of sub-polyhedric rock textures. When a packed aggregate of polyhedra is cut, a mosaic of individual polygons is obtained. Crystallographic concepts, enabling to predict what kinds of mosaics are obtained along any section plane in the polyhedral aggregate, are introduced. Thus, the shape (regular or irregular), the number of sides of the polygons in a given mosaic and likewise, the pattern of a mosaic — whether the mosaics made up of polygons of one type only, or a mixture of several types — can be determined by crystallographic operations. A few mosaics, obtained when packed aggregates of tetrakaidecahedra, rhombododecahedra, and cube-rhombododecahedra are cut along preferred planes of orientation, are presented. Geometric models are compared to the textural pattern of a few rocks, ceramics and metals. The frequency distribution of the mosaic types obtained by cutting across packed aggregates of tetrakaidecahedra is looked into it. Lastly, the spatial random distribution of two, and also the three mineral phases in the aggregate is graphically illustrated.