Gabbro
Gabbro is a compact, coarse-grained igneous rock igneous origin, ie a rock that is formed deep inside the earth.
Description of rock and mineral composition
Gabbro has a gray-black, sometimes blue-green color that results from the high proportion of dark-colored minerals such as pyroxene and olivine, of which it is mainly composed. The light fraction consists mainly of plagioclase feldspars. Quartz or a mineral from the group of feldspar can subordinate occur. In addition, the minerals hornblende, biotite, magnetite and ilmenite and accessory minerals such as pyrite, magnetite, apatite and more come before. With a presence of more than 5 percent orthopyroxene this rock is classified as Norit. In addition to the Noriten anorthosite and Hypertit belongs to the gabbros. They differ in the proportion of mafic minerals. With decreasing proportion of plagioclase gabbro blends smoothly in peridotite, the main constituent of the upper mantle.
Formation
Gabbro is found mainly in the oceanic crust, rarely also in the Continental. It is formed by the slow cooling basaltic magma usually more than five miles deep, often plutons occur ( broad masses of plutonic rock ). A recently he emerges mainly at mid-ocean ridges by slow crystallization of ascending mantle material. A gravity-induced separation of the crystallizing minerals can occasionally lead to layered gabbro rocks. Some of these Gabbrovorkommen within the continental crust may go to the differentiation of acidic magmas back ( resin). Within a larger quartz-rich magma chamber to form relatively small scale and basic, quartz- poor or - free rocks, like other radicals from continent - continent collisions be (including accretionary wedges ).
Classification
Because the stock of felsic minerals in the gabbro is QAPF classification chart on pages maximum Plagioklasführung. Gabbro s.str. (0-5 % quartz) goes on with increasing quartz content in Quarzgabbro. Contains the rock instead feldspar, one speaks of foidführendem gabbro. Nephelingabbro Theralith, Analcimgabbro Teschenit is called. Other types can be distinguished by the ratio of mafic minerals ( Fig. ). Diverting about rising Olivingehalt over to Olivingabbro and Troktolith.
As Mikrogabbro transition occurring shaped gabbro are called. This term refers only to the deposit situation of the rock body.
Occurrence
Gabbrovorkommen are distributed worldwide. Gabbro occurs in Germany in the Harz near Bad Harzburg, in the Odenwald ( Franken Steiner Pluton ) and Furth im Wald between high arch and the Czech border before. A very small deposits are found also in the Black Forest in Ehrsberg.
Well-known and large deposits are in South Africa to Rustenburg, in India in the state of Andhra Pradesh and Greenland in the Skaergaard complex.
Use and naming
Gabbro is used as a building material in the outer ( facades, staircases and flooring ) and indoors ( stairs and flooring, window sills ) and for grave times. All types of processing of these natural stones are from the grinding, polishing possible to flaming. Gabbro are also used for gravel and as construction material.
Gabbro was first named by the German geologist Christian Leopold von Buch after a town in Rosignano in the Italian region of Tuscany. Since gabbros have similar properties to granite, they are often heard of rock skilled rather reluctantly, referred to as black granite.
Natural stone types
- Star Galaxy (India, Andhra Pradesh )
- Belfast Black (South Africa)
- Nero Impala (South Africa)
- Nero Assoluto Z ( Zimbabwe)
Pictures
Pattern: Impala Dark
Gabbro quarry for construction material in Bad Harzburg