From Online Dictionary of Crystallography
Revision as of 11:27, 5 October 2017 by MassimoNespolo (A couple of languages added)
صنف أو مجموعة الفضاء (Ar); Groupe d'espace (Fr); Raumgruppe (Ge); Gruppo spaziale (It); 空間群 (Ja); Кристаллографическая группа (Ru); Grupo espacial (Sp).
The symmetry group of a three-dimensional crystal pattern is called its space group. In E2, the symmetry group of a two-dimensional crystal pattern is called its plane group. In E1, the symmetry group of a one-dimensional crystal pattern is called its line group.
To each crystal pattern belongs an infinite set of translations T, which are symmetry operations of that pattern. The set of all T forms a group known as the translation subgroup T of the space group G of the crystal pattern. T is an Abelian group and a normal subgroup of the space group. The factor group G/T of a space group G and its translation subgroup is isomorphic to the point group P of G.