An example of the rhombohedral crystals, quartz

In crystallography, the rhombohedral (or trigonal) crystal system is one of the seven lattice point groups, named after the two-dimensional rhombus. A crystal system is described by three basis vectors. In the rhombohedral system, the crystal is described by vectors of equal length, of which all three are not mutually orthogonal. The rhombohedral system can be thought of as the cubic system stretched diagonal along a body. a = b = c; . In some classification schemes, the rhombohedral system is grouped into a larger hexagonal system. For other uses, see Quartz (disambiguation). ... Image File history File links No higher resolution available. ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a point fixed while moving each atom of the crystal to the position of an atom of the same kind. ... Two rhombi. ... For other uses, see Crystal (disambiguation). ... This article is about vectors that have a particular relation to the spatial coordinates. ... In mathematics, two mathematical objects are considered equal if they are precisely the same in every way. ... For other uses of this word, see Length (disambiguation). ... In mathematics, orthogonal is synonymous with perpendicular when used as a simple adjective that is not part of any longer phrase with a standard definition. ... A diagonal can refer to a line joining two nonadjacent vertices of a polygon or polyhedron, or in contexts any upward or downward sloping line. ... In crystallography, the hexagonal crystal system is one of the 7 lattice point groups. ...

There exists only one rhombohedral Bravais lattice. In geometry and crystallography, a Bravais lattice, named after Auguste Bravais, is an infinite set of points generated by a set of discrete translation operations. ...

List of particulars

The point groups which fall under this crystal system are listed below, followed by their representations in international notation (Hermann-Mauguin notation) and Schoenflies notation, and example crystals. Hermann-Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. ... In crystallography, a crystallographic point group or crystal class is a set of symmetry operations that leave a point fixed, like rotations or reflections, which leave the crystal unchanged. ...

Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ... For other uses, see Hematite (disambiguation). ... The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. ... Alunite, or alumstone, is a mineral that was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. ... For other uses, see Dolomite (disambiguation). ... Ilmenite is a weakly magnetic iron-black or steel-gray mineral found in metamorphic and igneous rocks. ... For other uses, see Quartz (disambiguation). ... Cinnabar, sometimes written cinnabarite, is a name applied to red mercury(II) sulfide (HgS), or native vermilion, the common ore of mercury. ...

See also

• Crystal structure

Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., pp. 78 - 89, ISBN 0-471-80580-7