Rock-forming mineral

In geology, a rock-forming mineral is a mineral that builds up most of the earth's crust using the rock formed from it .

Use of the term

Regardless of the fuzzy definition, which, depending on the author, includes between 30 and 250 (according to other sources even up to 400) minerals, the term is used very often in the geosciences, as the determination of rock-forming minerals for the classification and naming of rocks, in particular of igneous rocks (which are classified according to their mineral composition in the route iron diagram ) and metamorphic rocks (in which the dominant mineral phases are included in the rock names), is indispensable. When analyzing a rock, the rock-forming minerals are divided into main mix parts (more than 10% by volume), secondary parts (between 1 and 10% by volume) and accessories (less than 1% by volume) based on their frequency .

Frequency distribution in the earth's crust

According to a model calculation, it can be assumed that ten minerals or groups of minerals make up around 95% of the volume of the earth's crust (modified from):

Mineral / group	Vol%
Plagioclase	39.0
Alkali feldspar	12.0
quartz	12.0
Pyroxenes	11.0
Amphiboles	5.0
mica	5.0
Olivine	3.0
Clay minerals including chlorite	4.5
Calcite / aragonite / dolomite	2.0
Magnetite including titanomagnetite	1.5
Other	4.9

determination

Only a small part of the rock-forming minerals can be determined macroscopically in the terrain if the individual mineral grains in the rock in question reach a size that allows criteria such as color, luster, fissibility, hardness, twinning and the like to be seen with the naked eye or to be assessed with a magnifying glass. For fine-grained rocks as well as for the rest of the rock-forming minerals in general, the investigation methods of rock microscopy with the polarization microscope , investigations with the microprobe or the use of X-ray methods are required.

literature

Roland Vinx: Rock determination in the field . 3. Edition. Spectrum, Heidelberg 2011, ISBN 978-3-8274-2748-9 .
Walter Ehrenreich Tröger: Optical determination of the rock-forming minerals . 2nd Edition. Part 2. Schweitzerbart, Stuttgart 1969, DNB 458442976 .

Individual evidence

^ Frank Press, Raymond Siever: General geology . 5th edition. Springer, Berlin 2008, ISBN 978-3-8274-1812-8 , pp. 61 .
^ Lexicon of Geosciences . 1st edition. tape 2 . Spectrum, Heidelberg 2000, ISBN 3-8274-0421-5 , p. 309 .
↑ Tom McCann, Mario Valdivia Manchego: Geology in the field . Springer Spectrum, Berlin, Heidelberg 2015, ISBN 978-3-8274-2382-5 , pp. 2-3 .

[Press/Siever-1] Frank Press, Raymond Siever: General geology . 5th edition. Springer, Berlin 2008, ISBN 978-3-8274-1812-8 , pp. 61 .

[2] Lexicon of Geosciences . 1st edition. tape 2 . Spectrum, Heidelberg 2000, ISBN 3-8274-0421-5 , p. 309 .

[McCann/Manchengo-3] Tom McCann, Mario Valdivia Manchego: Geology in the field . Springer Spectrum, Berlin, Heidelberg 2015, ISBN 978-3-8274-2382-5 , pp. 2-3 .