An ultramafic rock , ultramafitite or holomelanocrates rock is an igneous rock that consists of 90 percent by volume or more of mafic minerals , i.e. H. whose color index is M> 90. The rock can be monomineral or consist of several mafic minerals such as pyroxene , amphibole , olivine and the like. a. exist in changing circumstances. The olivine of the ultramafite can be transformed into serpentine . Usually the term is also applied to metamorphic rocks which have emerged from igneous rocks and which meet this criterion.
The naming of ultramafitites is not possible in the QAPF or route iron diagram due to the extremely low proportion of minerals considered there. Therefore, it is classified according to schemes based on the aforementioned mafic minerals.
Examples of plutonic Ultramafitite are pyroxenite (only pyroxene), hornblendite (only hornblende), glimmerite (only mica ) and peridotite (pyroxene and olivine) with the lower forms Lherzolite , harzburgite , wehrlite and dunite (the latter with more than 90% olivine).
Ultramafitites are often fragments of the earth's mantle that came to the earth's surface through geological processes, such as the olivine bombs of the Eifel or rock scales in orogen ( ophiolites ). The accumulation of early crystallizates at the bottom of a magma chamber can also lead to the formation of ultramafitites (e.g. Harzburgite ), where they can form significant deposits (e.g. Chromitites ) through the accumulation of ore minerals .
The term ultramafic rock is not the same as that of ultrabasic rock , so the two terms are not synonymous.
Natural stone types
Ultramafitite are used as decorative stones or as gravestones in the natural stone sector. Well-known varieties are the Solwark (peridotite from Norway) and the Poschiavo (serpentinitized peridotite from Switzerland).
- Myron G. Best: Igneous and Metamorphic Petrology . WH Freemann & Company, San Francisco 1982, ISBN 0-7167-1335-7 , pp. 37 .
- Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke Verlag, Stuttgart 1985, ISBN 3-432-94671-6 .
- Dietmar Reinsch: Natural stone studies. An introduction for civil engineers, architects, preservationists and stonemasons. P. 109, Enke, Stuttgart 1991, ISBN 3-432-99461-3