From Online Dictionary of Crystallography
Revision as of 08:48, 20 November 2017 by BrianMcMahon (Tidied translations.)
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.