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A crystal family is determined by lattices and point groups. It is formed by combining crystal systems that have space groups assigned to a common lattice system. In three dimensions, the hexagonal and trigonal crystal systems are combined into one hexagonal crystal family. Hexagonal hanksite crystal, with threefold c-axis symmetry
A crystal system is a set of point groups in which the point groups themselves and their corresponding space groups are assigned to a lattice system (see table in Crystal system#Crystal classes). The trigonal crystal system consists of the 5 point groups that have a single three-fold rotation axis, which includes space groups 143 to 167.
In Hermann–Mauguin notation, space groups are named by a symbol combining the point group identifier with the uppercase letters describing the lattice type.Translations within the lattice in the form of screw axes and glide planes are also noted, giving a complete crystallographic space group.
The triclinic crystal system class names, examples, Schönflies notation, Hermann-Mauguin notation, point groups, International Tables for Crystallography space group number, [1] orbifold, type, and space groups are listed in the table below. There are a total of 2 space groups.
Media in category "Trigonal minerals" The following 2 files are in this category, out of 2 total. Cinnabar on Dolomite.jpg 1,763 × 1,254; 1.4 MB.
Each crystallographic point group defines the (geometric) crystal class of the crystal. The point group of a crystal determines, among other things, the directional variation of physical properties that arise from its structure, including optical properties such as birefringency , or electro-optical features such as the Pockels effect .
Category: Trigonal crystal system. 7 languages. ... Chemical elements with trigonal structure (1 C, 2 P) T. Trigonal crystals (4 C, 2 P) Trigonal minerals (21 C, 200 ...
Crystal system Indicatrix Optical sign Birefringence Color in plain polars ... Trigonal: Uniaxial (-) 0.09: None Cristobalite: Tetragonal (pseudoisometric) Uniaxial ...