Pinacoid

Pinacoid with center of symmetry - (1) center of symmetry, (2) pair of faces of the pinacoid

The pinacoid (in ancient Greek πίναξ pínax "board, table") is a term from crystallography and describes a surface shape made up of two parallel surfaces. The connecting symmetry element is a center of symmetry , a twofold axis of rotation or a mirror plane. In most cases, these are areas with a special position that are parallel to two (in the hexagonal system, three) axes and intersect the third or fourth. Since the pinacoid is not a closed form, it can only occur in combinations. A crystal often consists of a prism and a pinacoid.

In the whirling crystal systems ( trigonal , tetragonal , hexagonal ) the pinacoid {001} or {0001} lies parallel to the plane of the minor axes (the base) and is therefore called the "basic pinacoid" (also base or straight end face ).
In the orthorhombic crystal system there is also a “macropinacoid” and a “brachypinacoid” located parallel to the macro- and brachydiagonal main section (also oblique end surface , transverse surface and longitudinal surface ).

The basic "orthopinacoid" {010} and a "clinopinacoid" {h0l} occur in the monoclinic crystal system .

In the triclinic crystal system the pinacoid is the eponymous general (and only) surface form {hkl} of the triclinic pinacoidal crystal class. All ideally shaped crystals of this crystal class represent a combination of pinacoids. Here (according to Ulan) a distinction can be made between basic, macro and brachypinatoid.

literature

Paul Ramdohr , Hugo Strunz : Textbook of Mineralogy . 16th edition. Ferdinand Enke, 1978, ISBN 3-432-82986-8 (p. 10 ff., P. 64 and 95)
Walter Borchardt-Ott: Crystallography . 6th edition. Springer, Berlin 2002, ISBN 3-540-43964-1 , pp. 31 and 70

Individual evidence

^ Wilhelm Gemoll: Greek-German school dictionary and concise dictionary . 10th completely revised edition. Edited and reviewed by Therese Aigner, Josef Bedrac, Renate Oswald, Jörg Schönbacher, Clemens Schuster, Rudolf Wachter, Franz Winter. Oldenbourg Schulbuchverlag, Munich a. a. 2006, ISBN 3-486-00234-1 .
↑ Pinakoīd . In: Brockhaus Konversations-Lexikon 1894–1896, Volume 13, p. 151.

[1] Wilhelm Gemoll: Greek-German school dictionary and concise dictionary . 10th completely revised edition. Edited and reviewed by Therese Aigner, Josef Bedrac, Renate Oswald, Jörg Schönbacher, Clemens Schuster, Rudolf Wachter, Franz Winter. Oldenbourg Schulbuchverlag, Munich a. a. 2006, ISBN 3-486-00234-1 .

[2] Pinakoīd . In: Brockhaus Konversations-Lexikon 1894–1896, Volume 13, p. 151.