Explanation

Also called twin is a regular continuum formed by two or more crystal according to a certain symmetry law. The corresponding crystal plane, crystal edge, corner top and other elements of the two adjacent single crystals are not completely parallel, but the two monomer can overlap or be completely parallel to each other through a certain reflection, rotation, backward extension (inversion) and other symmetrical operations. For some minerals that often present twin, such as feldspar minerals, twin type is one of the important basis for identifying them. Twin also has a great influence on the application of some crystal, such as piezoelectric quartze, optical iceland spar, etc.

Classification