Textures Of Metamorphic Rocks

Typically this will be initially described as foliated or non foliated. Nonfoliated rocks commonly contain equidimensional grains of a single mineral such as quartz calcite or dolomite. Foliated metamorphic rocks have four distinguishable types of aligned textures and they normally have a banded or layered appearance.

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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.

Textures of metamorphic rocks. Even if a complex assemblage is not identifiable at the wellsite a combination of minerals and textures should allow the rock to be characterized. The texture of a metamorphic rock is both a description of its constituent minerals along with their arrangement and size. Metamorphic rocks with no visible preferred orientation of mineral grains have a nonfoliated texture. Atlas of metamorphic rocks and their textures.

The original rock is subjected to heat temperatures greater than 150 to 200 c and pressure 100 megapascals 1 000 bar or more causing profound physical or chemical change the protolith may be a sedimentary igneous or existing metamorphic rock. Metamorphic rocks arise from the transformation of existing rock types in a process called metamorphism which means change in form. Examples of such rocks are quartzite formed from a quartz sandstone and marble formed from a. These can range from textures similar to the original protolith at low grades of metamorphism to textures that are purely produced during metamorphism and leave the rock with little resemblance to the original protolith.

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. Minerals that form do so because the chemical elements necessary to form them are present in the protolith. Non foliated are formed as a result of tectonic movements or direct pressure which makes their formation highly dependent on their pre existing conditions. Examples include slate gneiss phyllite and schist.

Metamorphic rocks exhibit a variety of textures. The texture of a metamorphic rock is a unique product of its mineralogy and metamorphic conditions. Foliated textures result from a parallel arrangement of flat platy. Foliation is described as the existence or appearance of layers.