Texture Of Metamorphic Rocks

Foliated metamorphic rocks have four distinguishable types of aligned textures and they normally have a banded or layered appearance.

Texture of metamorphic rocks. The texture of a metamorphic rock is a unique product of its mineralogy and metamorphic conditions. Even if a complex assemblage is not identifiable at the wellsite a combination of minerals and textures should allow the rock to be characterized. Examples of such rocks are quartzite formed from a quartz sandstone and marble formed from a. Foliation is described as the existence or appearance of layers.

Non foliated are formed as a result of tectonic movements or direct pressure which makes their formation highly dependent on their pre existing conditions. Also of importance are the rock s extent of homogeneity i e uniformity of composition throughout and the degree of. Foliated textures result from a parallel arrangement of flat platy. Metamorphic rocks with no visible preferred orientation of mineral grains have a nonfoliated texture.

A granular texture is developed if a rock s chemical composition is close to that of a particular mineral. The texture of a rock is the size shape and arrangement of the grains for sedimentary rocks or crystals for igneous and metamorphic rocks. Examples include slate gneiss phyllite and schist. Textures textures of metamorphic rocks fall into two broad groups foliated and non foliated foliation is produced in a rock by the parallel alignment of platy minerals e g muscovite biotite chlorite needle like minerals e g hornblende or tabular minerals e g feldspars.

Metamorphic rocks have been variously classified on the basis of texture and structure degree of metamorphism mineralogical composition and mode of origin etc. Minerals that form do so because the chemical elements necessary to form them are present in the protolith. The texture of a metamorphic rock is both a description of its constituent minerals along with their arrangement and size. Granular this describes a metamorphic rock consisting of interlocking equant crystals granules almost entirely of one mineral.

Typically this will be initially described as foliated or non foliated. A very general two fold classification based on the presence or absence of layered structure or foliation as defined above is as follows. In general the grain size of metamorphic rocks tends to increase with increasing grade of metamorphism as seen in the progression form fine grained shales to coarser but still fine grained slates to coarser grained schists and gneisses. Although textures and structures of the protolith are usually destroyed by metamorphism we can still get an idea about the original rock from the minerals present in the metamorphic rock.