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In geometry, a trigonal trapezohedron is a polyhedron with six congruent quadrilateral faces, which may be scalene or rhomboid. [1] [2] The variety with rhombus-shaped faces faces is a rhombohedron. [3] [4] An alternative name for the same shape is the trigonal deltohedron. [5]
Crystals can be classified in three ways: lattice systems, crystal systems and crystal families. The various classifications are often confused: in particular the trigonal crystal system is often confused with the rhombohedral lattice system, and the term "crystal system" is sometimes used to mean "lattice system" or "crystal family".
It can be used to define the rhombohedral lattice system, a honeycomb with rhombohedral cells. A rhombohedron has two opposite apices at which all face angles are equal; a prolate rhombohedron has this common angle acute, and an oblate rhombohedron has an obtuse angle at these vertices.
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. These 5 point groups have 7 corresponding space groups (denoted by R) assigned to the rhombohedral lattice system and 18 corresponding space groups (denoted by P) assigned to the hexagonal lattice system.
Some people certainly class the trigonal system as a kind of subset of the hexagonal. However, at the moment, there is an omission in the coverage of the crystal systems: within the trigonal system there are both primitive (P-centered) and rhombohedral (R-centered) lattices. At the moment a search for "trigonal" redirects you to "rhombohedral".
In the photo, Wright is shown at a Halloween party with her legs wrapped around a male friend dressed in an NFL costume. "At least it wasn't your son this time," one person wrote in the comments.
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.
Some species of male birds dance to impress their mates, such as the complicated dance routine of the little red-capped manakin or the flashy display of the male peacock. In other species, the ...