What are the characteristics of gneiss?

What are the characteristics of gneiss?

Gneiss is a medium- to coarse-grained, semischistose metamorphic rock. It is characterized by alternating light and dark bands differing in mineral composition (coarser grained than schist). The lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite.

What is gneiss composed of?

Gneiss is a coarse to medium grained banded metamorphic rock formed from igneous or sedimentary rocks during regional metamorphism. Rich in feldspars and quartz, gneisses also contain mica minerals and aluminous or ferromagnesian silicates.

What is the main textural characteristic of gneiss?

Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage. Gneisses are common in the ancient crust of continental shields.

What is unique about gneiss?

Gneiss is distinguished from other rocks because of the bands inside, which are due to the non-uniform distribution of the minerals during its formation, and therefore the bands differ in width. In suitable conditions, gneiss can be recrystallized into granite.

What physical characteristic distinguished the gneiss from the granite?

Appearance. Gneiss has alternating dark and light bands while granite has a coarse grain structure.

What is the main textural characteristic of gneiss quizlet?

What is the main textural characteristic of gneiss? Dark and light minerals are segregated in bands. During hydrothermal metamorphism the bulk composition of the rock does not change because it is simply a re-crystallization process.

How does gneiss turn into granite?

It is a high-grade metamorphic rock in which mineral grains recrystallized under intense heat and pressure. 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.

How are granite and gneiss similar and different?

In simplified terms, you can think of gneiss as a metamorphic version of granite. Both gneiss and granite are made of feldspars, quartz, mica, and smaller amounts of dark colored minerals like hornblende. The difference between granite and gneiss is in their overall texture and movement. Granite is evenly speckled.