Rhombohedral crystal system

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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, none of which are orthogonal. The rhombohedral system can be thought of as the cubic system stretched diagonally along a body. a = b = c; $\alpha, \beta, \gamma \neq 90^\circ$ . In some classification schemes, the rhombohedral system is grouped into a larger hexagonal system.

There exists only one rhombohedral Bravais lattice.

[edit] 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.

name	international	Schoenflies	examples
rhombohedral holohedral	$\overline{3}m$	D_3d	calcite, corundum, hematite
rhombohedral hemimorphic	$3 m$	C_3v	tourmaline, alunite
rhombohedral tetartohedral	$\overline{3}$	S₆	dolomite, ilmenite
trapezohedral	$32$	D₃	quartz, cinnabar
rhombohedral tetartohedral	$3$	C₃	none verified