Syenite
Syenites (after the ancient Egyptian site Syene ) form a closely related group of deep rocks (plutonites), which are referred to as the syenite / monzonite family. Syenites and monzonites are rich in feldspars and (compared to granites ) poor in quartz . Monzonites differ from the syenites in that the plagioclase feldspars outweigh the potash feldspars.
Mineral inventory
Syenite is chemically identical to the volcanic trachyte and represents its solidified equivalent in the earth's crust . Syenite is in field 7 in the classification diagram according to Fahrtisen .
The main mineral in syenite is alkali feldspar (orthoclase or microcline), the proportion of sodium-rich to intermediate plagioclase is lower . If the alkali feldspar clearly predominates (90 percent by volume) over the plagioclase, it is an alkali feldspar syenite . If quartz is added up to 20%, it is referred to as quartz syenite or quartz alkali feldspar syenite ; with a foid content of up to 10% from a foid-bearing syenite or foid-bearing alkali feldspar syenite . Mafish minerals such as biotite , hornblende , clinopyroxene or olivine usually only occur in small quantities.
Rock description and names
Syenite is a medium to coarse-grained igneous rock . Due to the mineral content , the syenite usually has a light gray or reddish color, but can occasionally be very dark. The directionless grainy structure is very similar to that of granite . Although mostly medium to coarse-grained, Syenite can also form fine-grained aplitic or giant -grained pegmatitic ducts .
Since it used to be difficult to determine exactly Syenites, there are variety names for groups of Syenites such as Larvikite (with anorthoclase ), Nordmarkite (with microcline ), Pulaskite (with nepheline ) and Lusitanite (with microcline).
Occurrence and use
Syenit is common worldwide. It usually occurs together with other plutonic rocks ( granite , granodiorite ), but is clearly subordinate to these in terms of quantity. In Germany he can be found u. a. in the Odenwald , Black Forest , Thuringian Forest and especially in Upper Lusatia . Other known occurrences can be found in, among others, Norway near Larvik .
Syenite is hard and can be polished and, in addition to being used as a building block, it also serves as a starting material for stone carving such as columns, slabs, plinths and the like. Many works of art from ancient times are made of syenite, which is found in Egypt (on Sinai ) by name (even if the stone from the city of Syene is a granite rather than a syenite according to the mineral content).
Natural stone types
- Cardinal Red (South Africa)
- Balma (Balma near Biella , Piedmont in Italy)
- Larvikites
See also
Web links
literature
- Roland Vinx: Rock determination in the field . Springer-Verlag, Berlin Heidelberg 2008, ISBN 3-8274-1513-6 .