Two or more different kinds of crystals formed, non-parallel with the living body of law. Also known as the twins. In the corresponding crystal face constitute double crystal single crystal between two energy-saving materials, will have a portion of the corresponding crystal edge parallel to each other but not all parallel one by one, but they will be reflected by a rotation of 180 ° or anti-stretch (Irony) of symmetry operations to achieve coincide with each other or completely parallel. Double crystal element refers to characterize the imaginary geometric elements in symmetric double crystal orientation relationship between the orientation of the single crystal. It comprises: twin planes, for an imaginary plane. Reflected by its constitution allows two single crystal twinning coincide or completely parallel. Thus, the twin plane lattice must be both equal and parallel to a mutually consistent public face net. Symbolic form direction with parallel twin planes in a crystal plane or perpendicular to a zone axis to represent. Such as cassiterite geniculate double-crystal (Figure 1 cassiterite geniculate twinning), twin plane ‖ (101); orthoclase of Carlsbad twinning law (Figure 2 orthoclase of Carlsbad twin law Crystal), twin plane ⊥ (001). Twin plane can never be parallel to the single crystal of the symmetry plane, otherwise the two single crystals in a completely parallel to constitute a parallel relationship with students. Twin crystal axis, an imaginary straight line. When rotated by 180 ° around it, can constitute a single crystal twinning of two coincident or parallel to achieve complete agreement. Therefore, two crystal axes must be a reciprocal lattice both equal and parallel to the same public ranks. Twin crystal axis direction with a particular zone axis parallel or perpendicular to the crystal plane of a particular form of symbols represented. For example Carlsbad twinning law ‖ twin crystal axis (001); geniculate twin crystal twinning axis ⊥ (101). Double crystal axis must not parallel to the single crystal of the even symmetry axis. Twinning center for an imaginary point. Through its anti-stretch after double-crystal monomer can form two overlap or reach consensus parallel orientation (Figure 3 tetrahedrite twinning (circles represent double crystal center)). Bimorph center possible only appear in a single crystal itself has no center of symmetry of the case; and in general, it is just a derivative of the double-crystal elements, it can not be considered. Variants by homogeneous transformation and becomes more like a low double-crystal symmetry degree low temperature variants generated. Slip twinning, generally by mechanical stress after the formation of crystals, in part of a series of adjacent lattice plane interworking simultaneous uniform slip plastic deformation, so that part is not crystal slip and slip part Formed by twinning relationship between new material, so called mechanical twinning or deformation twinning. Slip twinning are expressed as polysynthetic twins, and some low-symmetry metal crystals commonly suffered regional metamorphism in some mineral crystals. In addition, some metal recrystallization during the annealing process Shandong days Yue, by varying the particle diffusion and intergranular interface, easy to produce double-crystal joints instead of the general intergranular annealed to form double-crystal interface. It is almost confined there fcc lattice of metal. Twinning probability distribution in a variety of crystal, double-crystal is very inconsistent. Such as calcite, cassiterite, staurolite and other minerals twinning common, things do not be - and igneous quartz plagioclase almost without exception, showed a double-crystal output; but in most species do not appear crystal twinning or twinning rare. Twinning distributed in each crystal system is not balanced, the largest double-crystal belongs to monoclinic and orthogonal (oblique) crystal system, followed by three oblique and constituents, isometric, tetragonal. Twin hexagonal crystal are very rare. These phenomena and the characteristics of the crystal structure and symmetry of the crystal system is closely related. Significance of double-crystal twinning often has some mineral output, double-crystal is to identify one of the main features of these minerals can be determined according to the crystal orientation in space. Slip twinning emergence also has genetic significance. Exists for the use of twin crystals crystals are generally detrimental. Such as crystal, having Dauphine twinning law Yue Crystal Materials Co., Ltd. Shandong days, plus or minus two single crystals in upright axis of good contrast, the piezoelectric effect cancel each other out and not be used as a piezoelectric material; when there is a double Brazilian law Crystal, the two single crystal optical direction is just the opposite, neither as a piezoelectric material, it can not be used as an optical material. Individual twinning, as Dauphine twinning crystal, can be manually eliminated (see quartz group minerals). New materials, Shandong days Yue, energy-saving materials provided by Jinan Spark Technology Development Company Limited. Jinan Spark Technology Development Co., Ltd. (www.sicc.cc) (www.sicc.cc) strong, credible, in Jinan, Shandong chemical equipment industry has accumulated a large number of loyal customers. 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