P.B.C.-vector analysis by Fourier transform of morphology. On crystal growth of monoclinic potassium feldspars*

Abstract

Abstract The morphological lattice of monoclinic potassium feldspars is a P-lattice with a/2 and b/2 and co-ordinates 1/41/41/4. The reciprocal crystal has 8 faces and symmetry 2/m. The morphological units (KT4O8, T = A1, Si) are connected over T – O bonds along [100], [010] and [102] and over K – O bonds along [001]. The arrangements of the polyhedra parallel to the crystal faces show that (001), (010), (100), ([unk]01), (110) and ([unk]11) are F-faces and ([unk]01), (130) and (021) S-faces according to Hartman and Perdok. Considering the morphological extinction rules (110) has to be regarded as an S-face and ([unk]11) as a K-face. The areas of the net meshes divided by the number of the morphological units per growth layer correspond to the attachment energies, the quotients are proportional to the central distances of the reciprocal morphological lattice. The thickness of the growth layer is determined by the extinction rules. By a Wulff-plot a growth form is obtained which shows all the important faces.