Difference Between Gneiss and Granite

Gneiss vs Granite

There are many different types of rocks found on planet earth. The differences mainly pertain to composition of minerals, texture, color, hardness, size of grains, and their permeability. However, for the purpose of classification to make their study easier, all rocks have been divided into three major types namely igneous, sedimentary, and metamorphic rocks. Granite is an igneous rock while gneiss is a rock that may have been igneous or sedimentary earlier but has undergone metamorphic process. There are similarities between the two types of rocks confusing many people. This article attempts to highlight their differences.

Granite

Granite is a hard igneous rock that is mostly made up of feldspar and quartz. Granite has a crystalline structure, and it can have a wide range of colors from grey to pink. The color of a granite rock is dependent upon the composition of minerals. Any igneous rock that contains one fifth of quartz is labeled as granite. The pink shade of many granite rocks is because of the presence of alkali feldspar. Granite is found inside the crust of the earth and has magmatic origins.

Gneiss

Gneiss is a hard rock that has a mineral composition similar to granite as it contains the feldspar, mica, and quartz. This is a rock that is formed from pre-existing igneous rocks such as granite that have been subject to conditions of high pressure and temperature. The nomenclature of gneiss is done on the name of the rock whose metamorphosis leads to its formation. Thus, we have granite gneiss, diorite gneiss, and so on. This lets us know the parent rock that was converted into gneiss because of the effects of temperature and pressure.

What is the difference between Gneiss and Granite?

• Granite is an igneous rock, whereas gneiss is formed after metamorphosis of an existing igneous rock.

• The mineral composition of both granite and gneiss is same but alteration of granite because of very high pressure and temperature leads to the formation of gneiss.

• Not all gneiss is obtained from granite, and there are also diorite gneiss, biotite gneiss, garnet gneiss, and so on.

• Minerals are seen arranged in bands, in gneiss.

• Though gneiss is sometimes labeled under the broad category of granite by those selling the rock, it is not same as granite.