# Difference between revisions of "Ogdohedry"

### From Online Dictionary of Crystallography

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The point group of a crystal is called ogdohedry if it is a subgroup of index 8 of the point group of its lattice. | The point group of a crystal is called ogdohedry if it is a subgroup of index 8 of the point group of its lattice. | ||

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+ | In the three dimensional space there is only one ogdohedry: it corresponds to the [[geometric crystal class]] 3 of crystals belonging to the hexagonal [[lattice system]] (in case rhombohedral crystals, it corresponds instead to a [[tetartohedry]]). | ||

== See also == | == See also == |

## Revision as of 17:49, 2 March 2007

Ogdoédrie (*Fr*). Ogdoedria (*Sp*). Ogdoedria (*It*)

## Definition

The point group of a crystal is called ogdohedry if it is a subgroup of index 8 of the point group of its lattice.

In the three dimensional space there is only one ogdohedry: it corresponds to the geometric crystal class 3 of crystals belonging to the hexagonal lattice system (in case rhombohedral crystals, it corresponds instead to a tetartohedry).

## See also

Section 9.1 of *International Tables of Crystallography, Volume A*