Psephit
Psephit ( Greek psẽphos " little stone") is the name for coarse clastic sedimentary rocks with grain sizes over 2 mm. According to the geotechnical grain size classification , this corresponds to the stone sizes of gravel as well as conglomerates and breccias . The term can be used independently of the material, i. H. not only for clastic silicate rocks, but also for clastic carbonate rocks. However, the term Kalkpsephit is hardly used. In the carbonate petrography, a limestone of this grain size is called Kalkrudite . In the case of a metamorphosis , Psephites are given the prefix Meta -, they become Metapsephites .
The coarse-grained raw material comes from the mechanical destruction of other rocks. This happens, for example, by frost blasting rock walls and blocks so that the fragments collect as rock debris in rubble or block heaps . By river transport, sharp-edged rock fragments are converted into rubble .
In addition to the coarse-clastic psephite, a distinction is made between fine-clastic pelites (with grain sizes below 0.02 mm, e.g. clays) and medium-clastic sedimentary rocks ( psammites ) with grain sizes ranging from 0.02–2 mm (coarse silt to coarse sand). As an alternative to the Pelit / Psammit / Psephit scheme for naming siliciclastic sedimentary rocks according to grain sizes, the terms claystone / siltstone / sandstone / conglomerate or breccia are used. In carbonate petrography, the term trio lutite / arenite / rudite is used much more often to describe or name rocks according to grain size.
literature
- Hans Murawski , Wilhelm Meyer : Geological dictionary . 11th, revised and expanded edition. Elsevier, Spektrum Akademischer Verlag, Munich 2004, ISBN 3-8274-1445-8 , pp. 112, 118 and Tab. VI 1–12 .
- Hans Füchtbauer : sandstones. In: Hans Füchtbauer (Hrsg.): Sediments und Sedimentgesteine (= Sediment-Petrologie. Vol. 2). 4th, completely revised edition. Schweizerbart, Stuttgart 1988, ISBN 3-510-65138-3 , pp. 97-183.
Remarks
- ↑ Gravel: average stone diameter 2–63 mm