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  2. Trigonal trapezohedron - Wikipedia

    en.wikipedia.org/wiki/Trigonal_trapezohedron

    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]

  3. Hexagonal crystal family - Wikipedia

    en.wikipedia.org/wiki/Hexagonal_crystal_family

    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.

  4. Rhombohedron - Wikipedia

    en.wikipedia.org/wiki/Rhombohedron

    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.

  5. Crystal structure - Wikipedia

    en.wikipedia.org/wiki/Crystal_structure

    In monoclinic, trigonal, tetragonal, and hexagonal systems there is one unique axis (sometimes called the principal axis) which has higher rotational symmetry than the other two axes. The basal plane is the plane perpendicular to the principal axis in these crystal systems.

  6. Periodic table (crystal structure) - Wikipedia

    en.wikipedia.org/wiki/Periodic_table_(crystal...

    Rhombohedral: R 3 m (No. 166) 105 (rh.) 315 (hex.) Partly due to its complexity, whether this structure is the ground state of Boron has not been fully settled. α-As: A7: Rhombohedral: R 3 m (No. 166) 2 (rh.) 6 (hex.) in grey metallic form, each As atom has 3 neighbours in the same sheet at 251.7pm; 3 in adjacent sheet at 312.0 pm. [18]

  7. Trigonal trapezohedral honeycomb - Wikipedia

    en.wikipedia.org/wiki/Trigonal_trapezohedral...

    In geometry, the trigonal trapezohedral honeycomb is a uniform space-filling tessellation (or honeycomb) in Euclidean 3-space. Cells are identical trigonal trapezohedra or rhombohedra . Conway, Burgiel, and Goodman-Strauss call it an oblate cubille .

  8. Parallelepiped - Wikipedia

    en.wikipedia.org/wiki/Parallelepiped

    The parallelepiped with D 3d symmetry is known as a trigonal trapezohedron, which has six congruent rhombic faces (also called an isohedral rhombohedron). For parallelepipeds with D 2h symmetry, there are two cases: Rectangular cuboid: it has six rectangular faces (also called a rectangular parallelepiped, or sometimes simply a cuboid).

  9. Dolomite (mineral) - Wikipedia

    en.wikipedia.org/wiki/Dolomite_(mineral)

    The mineral dolomite crystallizes in the trigonal-rhombohedral system. It forms white, tan, gray, or pink crystals. It forms white, tan, gray, or pink crystals. Dolomite is a double carbonate, having an alternating structural arrangement of calcium and magnesium ions.