Font granite
As Schriftgranit ( synonymous rune and pegmatite ), a usually granitic or syenitic igneous rock with a special structure known as the regular, so-called graphical adhesions eutectic structure of quartz and feldspar is characterized. It arises from the rapid crystallization of a melt in the eutectic and is known in a similar form, for example from metallurgy. The quartz and feldspar components behave like crystallographic single crystals with skeletal growth and mutual interpenetration of the two phases (and show, for example, uniform extinction under the polarization microscope). However, between the quartz phase and the feldspar phase there is no regular intergrowth in the sense of an epitaxy , which is easy to see given the completely different crystal structure of quartz and feldspar. The name is based on the fact that these adhesions are often reminiscent of runes or similar characters. Writing granite often forms in the late crystallization phase of a magma , for example in pegmatites.
History
The term granite writing was first introduced into the scientific literature in 1827 by Karl Caesar von Leonhard .
distribution
Font granite is common worldwide and occurs regularly in the central zones of large granite bodies , e.g. B. in Brocken granite. However, it only takes up smaller areas within it. Font granite is also not uncommon as Scandinavian debris in northern Germany.
use
Writing granite is processed into tumbled stones and small art objects. Colloquially, the term zebra feldspar is used for very coarse-grained writing granite , as the "writing" cannot be recognized in normal-sized pieces.
literature
- Maresch, W & Medenbach, O .: Steinbach's natural guide rocks, Mosaik Verlag Munich, 1987. ISBN 3-576-10699-5