These rocks are known as granitoids (rocks resembling granite) because it may not be easy to distinguish different feldspar group minerals in the hand sample. See the diagram below:Ĭlassification of granite (red field) and granitic rocks (red+yellow) is based on the content of quartz (Q) (in relation to feldspar) and the mineralogy of the feldspar group minerals (A and P). Granitic rocks which contain less than 10% plagioclase feldspar are named alkali feldspar granite and granitic rocks where the dominant feldspar is clearly plagioclase (over 65%) are named either granodiorite (65-90% of feldspar is plagioclase) or tonalite (over 90% of feldspar is plagioclase) 2. Rocks which fulfil the quartz content requirement but have a different ratio of feldspars have different names although they are known as granitoids or granitic rocks too.
![granite samples granite samples](https://st4.depositphotos.com/10634550/20723/i/1600/depositphotos_207238594-stock-photo-kitchen-counter-tops-color-samples.jpg)
Granite is a coarse-grained quartzo-feldspathic igneous rock which contains 20-60% quartz of total quartz + feldspar (other minerals are neglected) and 35-90% of the feldspar is alkali feldspar (orthoclase or microcline). This article aims to explain what really is granite and what it is not. This rock name may well be the most abused geological term in existence. Width of view is about 50 cm.Īlthough it is indeed very widespread, not every rock that is named so is a true granite. It is crystalline (composed of visible mineral grains) and always contains quartz which usually is gray and also feldspar which is either reddish, white or yellow in most cases. This picture of a granite pegmatite from northern Norway (Nyelv) is very coarse-grained for a normal granite and compositionally simpler than most granite samples, but it illustrates well what granite is.
![granite samples granite samples](http://the-granite-shop.com/samples/DSC_0022.jpg)
These two are the most common minerals in the crust which means that granite too is among the most ubiquitous rock types, especially in the upper continental crust.
![granite samples granite samples](https://boutique.polycor.com/wp-content/uploads/2018/03/granite-sample-caledonia-polished-polycor.jpg)
Granite is a crystalline igneous rock that consists largely of feldspar and quartz.