What is Gneissosity?
In a metamorphic rock, commonly gneiss, the coarse, textural lineation or banding of the constituent minerals into alternating silicic and mafic layers. Synonym of: gneissosity.
What does schistosity mean in geology?
schistosity, mode of foliation that occurs in certain metamorphic rocks as a consequence of the parallel alignment of platy and lath-shaped mineral constituents. It reflects a considerable intensity of metamorphism—i.e., changes resulting from high temperatures, pressures, and deformation.
What is schistosity texture?
Schistosity – the layering in a coarse grained, crystalline rock due to the parallel arrangement of platy mineral grains such as muscovite and biotite. Other minerals present are typically quartz and feldspar, plus a variety of other minerals such as garnet, staurolite, kyanite, sillimanite.
What is gneissic banding?
The minerals in gneiss are arranged into layers that appear as bands in cross section. This is called gneissic banding. The darker bands have relatively more mafic minerals (those containing more magnesium and iron).
What is marble’s parent rock?
Limestone is a sedimentary rock that is composed of the mineral calcite. The presence of the foliated rock, likely slate, suggests that before this rock metamorphosed it was composed of limestone (the parent rock of marble) layered with small-grained sedimentary rocks, like siltstone or shale.
What is Crenulation cleavage?
In a geological context, crenulation or crenulation cleavage is a fabric formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions causing the formation of the superimposed foliations.
How do schists form?
Schist is medium grade metamorphic rock, formed by the metamorphosis of mudstone / shale, or some types of igneous rock, to a higher degree than slate, i.e. it has been subjected to higher temperatures and pressures. These larger crystals reflect light so that schist often has a high lustre, i.e. it is shiny.
What is slaty cleavage?
Slaty cleavage is a pervasive, parallel foliation (layering) of fine-grained platy minerals (chlorite) in a direction perpendicular to the direction of maximum stress. The process produces the rocks slate and phyllite. They represent slaty cleavage, developed when the rock was compressed and folded.
What is schistose rock?
What is phyllite parent rock?
phyllite, fine-grained metamorphic rock formed by the reconstitution of fine-grained, parent sedimentary rocks, such as mudstones or shales.
What is the gneiss parent rock?
Gneiss is a medium- to coarse-grained rock formed under high grade-metamorphic conditions. Gneiss is primarily composed of quartz, potassium feldspar, and plagioclase feldspar with lesser amounts of biotite, muscovite, and amphibole. Granites and sometimes rhyolite provide the parent rock for gneiss.