Banded Granite Gneiss

In the saxo thuringian there are intensely sheared banded gneisses after a coarse granite.

Banded granite gneiss.

Gneiss is formed by high temperature and high pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Orthogneiss is gneiss derived from igneous rock such as granite. Amphibolite gneiss or hornblende gneiss for example. The coarsely crystalline dark rock is the 1 4 billion year old oracle granite.

The term gneiss without any additional information is commonly imagined to be compositionally similar to granite k feldspar quartz biotite. It is important to note that gneiss is a rock type that is defined by its oriented texture rather by its mineralogy or chemical composition. Bezy j v 2016 a guide to the geology of the santa catalina mountains arizona. These photos are from the kadanie dam.

Gneiss usually is distinguished from schist by its foliation and schistosity. Banded gneiss on the catalina highway. Banded gneiss geology en ch academic ru. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct foliation.

A photograph of polished gneiss from the stock of a countertop vendor. Gneiss metamorphic rock that has a distinct banding which is apparent in hand specimen or on a microscopic scale. This banded gneiss underwent partial melting to form some beautiful migmatites with neatly spaced shear bands filled with leucosomes. Intense heat and pressure can also metamorphose granite into a banded rock known as granite gneiss this transformation is usually more of a structural change than a mineralogical transformation.

The granite gneiss composed of biotite k feldspars quartz and minor garnet occurs in close association with the banded gneiss. The light colored pegmatitic granitic rocks and quartz veins that intrude it are related to the 50 million year old wilderness suite leucogranites. Gneiss displays a well developed foliation and a poorly developed schistosity and cleavage. Gneiss forms at higher temperatures and pressures than schist.

Paragneiss is gneiss derived from sedimentary rock such as sandstone.