A rare assemblage of tellurides has been found in a vein of the Yokozuru mine, Sannotake skarn zone, North Kyushu. The tellurides are melonite, volynskite, hessite, and petzite whose compositions correspond to Ni_0.98 Te_2.00, Ag_0.99 Bi_1.01 Te_2.00, Ag_1.99 Te_1.01 and Ag_2.93 Au_1.03 Te_2.04 respectively. Some grains of hessite contain selenium up to 0.68 wt.% replacing tellurium. Optical properties are described for melonite and volynskite. Values of reflectance and microhardness were obtained upon melonite (VHN=67), volynskite (40–80), and siegenite (467–551).
Paragenetic relation suggests that the mineralization of the vein started with deposition of scheelite and quartz, followed by Cu–Bi–Fe sulfides, and ended with the rare mineral assemblage of Ni–Bi–Au–Ag–Te system.

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A computer program for crystal figure drawing has been written with BASIC language. The program deals with three kinds of drawing: (1) the stereographic projection of crystal faces, (2) the drawing of a single crystal figure and (3) the drawing of a twin crystal figure. Face data are given by the values of ρ and φ from goniometric measurements or by Miller indices (hkl) with the lattice constants. The projection (1) facilitates us to find out the symmetry and zones of a crystal to be drawn. In the drawing (2), it is possible to draw the crystal figure viewed from any arbitrary direction. The twin crystal figure (3) is composed of only two individuals.

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Symmetrizers are defined as such symmetry operations that contribute to enhancing the symmetry of the point group G_X of a crystal to that of G_D of its X-ray diffraction pattern when G_X<G_D. In order to look for possible types of symmetrizer, the crystal structure under consideration is assumed to consist of substructures identical to each other and distributed according to parallel shifts from one to the others. Such a structure is aptly described by a space groupoid, the substructures being the geometric representation of its kernel. It has been known that if the structure gives rise to an enhanced diffraction (vector) symmetry, the symmetry of the substructure is equal to the enhanced symmetry, and the conditions for the hull of the space groupoid to satisfy when the diffraction symmetry is enhanced are sought in the present study. From the consideration of the symmetry of the vector set in general, the relation of direct sum is derived. This relation is then applied to the hull of the present space groupoid, and it is concluded that if the relation of direct sum holds in the hull and if the vector subsets, each produced by a term in the direct sum, are symmetrically related to each other by an operation g, such a structure may be constructed as causing an enhanced diffraction symmetry, for which g is a symmetrizer.

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