Greenschist

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Greenschist rich in chlorite

Greenschists (engl .: greenschist ) is a metamorphic rock and belongs to the group of crystalline slate . It occurs together with gneiss , mica schist and phyllites . The name gives the mineral components involved in the mineral stock with a green color, such as chlorite, epidote, actinolite, green garnet and the like. a. (see below).

Origin and chemical composition

Greenschist are transformed, basic former deep rock ( gabbros ) and igneous rocks ( diabase , spilite , diabastuffe, etc.) as well as calcium and magnesium-rich sedimentites ( dolomite , dolomite-limestone marl, etc.). Places of education are the upper tectonic mountain levels. Under intensive folding processes at relatively low pressure and through the action of water, rock-forming silicates, mostly containing water (OH), are formed (see " Greenschist facies "). The water can be molecularly bound in the rock or it can be supplied in ascending order on tectonic structures . Chemically, they are low-silica, partly aluminum-rich (then low-magnesium) or low-aluminum (then magnesium-rich) shale rocks. The following table summarizes the chemical composition of some typical green slate representatives (in% by mass).

chem. connection Prasinite Epidote rock Talc slate Chlorite slate Magnetite-chlorite-schist Epidote chlorite schist Pot stone Talkmagne-sitfels
SiO 2 47 38 53 27 28 50 52 28
Al 2 O 3 20th 25th 4th 31 21st 16.5 2 0.5
Fe 2 O 3 4th 10 6th 20th 3 4th 4th 4th
FeO 4th - 1 1.5 15th 7th - 5.7
MgO 8th - 30th 11 19th 6th 29 33
CaO 11 23 1.5 1.7 2.5 7th 3 0.7
Na 2 O 2 - 1.5 2.8 0.2 3 - -
K 2 O 1.5 - 1.5 2.8 0.1 1 - -
H 2 O 2 2.6 2.5 3.8 10 4th 3 27
CO 2 - - - - - - - 27

Mineral inventory

Green- colored minerals such as chlorite , epidote , green hornblende (actinolite), green garnet , grossular , chloritoid are the main contributors to the composition . These form strongly varying mixtures with sericite , zoisite , albite , bytownite , calcite , dolomite , magnetite . As for ores, hematite , siderite , pyrite and pyrrhotite occur in green schists.
The following table provides an exemplary overview of the mineral inventory of various green slate deposits (according to Pfeiffer, kurz, Matthé 1985).

variety Chlorite Amphibole Epidote Albite Biotite carbonate quartz Accessories
Epidote chlorite schist (Furnlund, Norway) 30th 3 23 40 - 2 1 1
Greenschist (Frosktjernbekken, Norway) 5 35 10 35 10 - - 5
Greenshist (Mikulov, Czech Republic) 30-35 15-20 8-10 15th - - 15-25 -
Chlorite-epidote schist (Gory Czywczynskie, Poland) 18th - 70 - - - 10 2
Greenschist (Valais, Switzerland) 27 14th 21st 35 - - 2 1

Physical-technical properties

The values ​​listed in the following table apply as an example for chlorite slate (trade name "Verde Fundres"), Fundres quarry ( South Tyrol , Italy).

Gross density [kg / dm³] Compressive strength [MPa] Press. n. exposure to frost [MPa] Flexural strength [MPa] Minimum height of fall [cm]
2.62 ... 2.74 223 185 23 106
thermal expansion [mm / m / 10 ° C] Abrasion resistance [cm³ / 50 cm²] Abrasion resistance (AMSLER) [mm] Water absorption [wt .-%] Frost resistance
0.75 6.0 1.0 0.01 resistant

structure

Green slates are mostly soft rocks and sometimes feel greasy to the touch. The texture is predominantly slate, leafy and / or scaly. This results from the preferred orientation of the chlorite platelets and the mostly long-needle to fibrous amphiboles. Higher epidote proportions result in a more massive structure.

Occurrence

Green slate occurs worldwide in the core areas of eroded mountains. European deposits are the Saxon Granulite Mountains , the Saxon-Bohemian Ore Mountains , the Fichtel Mountains , the Bavarian Forest , Spessart , Odenwald and the Sudetes . There is also a wide distribution in the young Alpine chain mountains of Austria, Italy and France. Other commercially used deposits are located in Russia (Schabrowsk, Sysert , Yekaterinburg ).

use

  • Prasinit is occasionally used as a road building material (broken down into different grain sizes and sieved or mixed to defined grain sizes).
  • Chlorite slate is used as a stone in the construction industry due to its favorable processing properties (low hardness, ability to split and polish, suitability for sawing). It is suitable for the production of wall and curb stones, facade cladding and floor slabs, steps and tiles. Another use is for table tops and cover plates as well as in the stonemasonry trade. Particularly attractively patterned pieces are also used in the jewelry industry.

literature

  • H. Murawski, W. Meyer: Geological dictionary. Spektrum-Verlag, 2010, ISBN 978-3-8274-1445-8 .
  • R. Jubelt, P. Schreiter: Rock determination book. German publishing house for basic industry, Leipzig 1977, ISBN 3-7684-6244-7 .
  • F. Müller: INSK compact - the international natural stone index for the current market. Volume II, Ebner Verlag, Ulm 1997, DNB 953679284 .
  • L. Pfeiffer, M. Kurz, G. Mathè: Introduction to Petrology. Akademie-Verlag, Berlin 1985, DNB 860602648 .