Crystal forms of natural microdiamonds

Abstract

Geometrical crystallographic features of rare diamond micro-crystals (0.3–0.5mm in diameter) from kimberlites having different complex flat and smooth faces are described. Such polyhedrons of microdiamonds are typically composed of two or more combinations of seven different crystal forms belonging to hexoctahedral symmetry class: octahedron, cube, rhombic dodecahedron, trisoctahedron, trapezohedron, tetrahexahedron and hexoctahedron. Many of them are not yet known for macro-crystals of this mineral. All these forms are found as small faces on the octahedral crystals. Both flat and smooth faces of octahedron and cube on such crystals have their own growth sectors. Flat faces of rhombic dodecahedron, different trisoctahedrons, trapezohedrons and hexoctahedrons occur as so-called faces of degeneration of octahedral growth planes. Nature of tetrahexahedron flat faces is not clear. An investigation of the complex diamond polyhedrons should give a new idea on crystal morphology of diamond, make more precise its symmetry and be important for the explanation of the nature of diamond on the whole.