EVOLUÇÃO MORFOLÓGICA E TEXTURAL DE DIAMANTES BASEADA NO MÉTODO DA FOTOGONIOMETRIA.

Abstract

The curvilinear surfaces of 47 diamonds from Macaúbas river basin (MG) were studied on theparabolic goniometer. For the diamond description primary genetic value is given to the form of thecrystal, but the secondary is given to the sculpture of the surface. Crystallographic terms: octahedroid,dodecahedroid, cuboid are usually used for classification of the form of the diamonds. For practicalpurposes this is possible to consider reasonable. To determine the figure of the curve-faced crystal,the main indicator is the position of maximum of intensity of reflected light on the stereographicprojections of crystal, but not angular sizes of the reflex. Curvilinear faces of diamonds suggest theirdissolution processes. The symmetry of crystal shape Oh for such diamonds usually decreases to C2h,C3h or C4h, which explains a crystal rotation at the dissolution according to the P. Curie principle. Thecurvilinear surfaces of the diamond crystals are possible to describe by means of fragments of thesurfaces of triaxial ellipsoid duplicated with symmetry group Oh up to twelve. Ellipsoid have semiaxisA1, A2, A3, numbered in the order of their growth, and well-ordered relatively to the crystalstructure. Axis A2 is always directed along the axis L4, but two other axes are inclined to axis L2 underthe small angle (up to 7 degrees). Angle á defines an appearance of so called “face-seam” on thesurfaces of the diamond. There are 24 curvilinear surfaces formed the dodecahedroid with “faceseams”,as a limiting shape of the diamond dissolution. Ellipsoidal surface of the diamond is thedynamic indicator of stability of the crystal structure of a homoeopolar crystal to the processes ofdissolution and partly detrition. The existence of both a triangular etching pits with the flat bottomon the surfaces (111) and a negative relief of the surface for all directions <110> shows a regenerationprocess of a diamond.