Construction de mosaïques pour l'analyse des textures subpolyédriques

Abstract

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.

Fifty‐nine tetrakaidecahedra as grain models

“…In fact, it is just as an artificial shape as the above-mentioned packable forms. The actual patterns observed in the slides of rocks or polished sections of metals are always much more complicated than the simple hexagonal mosaic and even than the patterns obtained by cutting a close packing of tetrakaidecahedra (see Grolier & Hucher, 1973).…”