Acta Chim. Slov. 43 (1996) 319-341.
CORRESPONDENCE BETWEEN STRUCTURE AND MORPHOLOGY AND TWIN FORMATION
Institut Für Mineralogie und Mineralische Rohstoffe, Technische Universität, Adolph-Roemer-Str. 2A, 38678 Clausthal-Zellerfeld, Germany
The Fourier transform method of crystal morphology is a new procedure for studying growth phenomena. The plane indices of a crystal denote points of a lattice in reciprocal space. A Fourier transformation results in the morphological lattice. The reciprocal crystal is the Dirichlet domain polyhedron to the morphological lattice. The structural content of the reciprocal crystal is the growth unit. The bond strengths between neighbouring growth units are proportional to the plane areas of the reciprocal crystal, which is also designated as the energetic structure. The equilibrium form and the real growth form can be determined with the Fourier transform method. The method will be explained using monoclinic potassium feldspars as an example, whose tracht and habit vary according to temperature. Pseudosymmetries of the reciprocal crystal and thus the translation lattice are necessary prerequisites for twin formation and oriented intergrowths. As will be shown with sucrose, potassium bichromate and pentaerythrite, different growth mechanisms of twins are observed.