To be considered a crystal twin, more is required! The crystals cannot simply be randomly fused, but must be fused according to a specific twinning law. This law is a prerequisite for the existence of a crystal twin. The external shape of the twin is not the primary factor; this is merely a consequence of its internal structure. Twins form when two crystals are connected in such a way that they can be transformed into one another by reflection across a mirror plane or rotation around a common axis. The constituents of both crystals are arranged as mirror images of each other on either side of the twinning plane.
 A total of 110 pages in DIN A4 format. Paperback, with countless color photos and illustrations! 2017