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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, 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; $\alpha = \beta = \gamma \neq 90^\circ$ . In some classification schemes, the rhombohedral system is grouped into a larger hexagonal system.

There exists only one rhombohedral Bravais lattice.

List of particulars

The point groups which fall under this crystal system are listed below, followed by their representations in international notation and Schoenflies notation, and example crystals.

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

References

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

This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia

Trigonal

List of particulars

See also

References