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Granit, başlıca kuvars ve alkali feldispat içeren ve tüm feldispatlarının içindeki plajiyoklaz miktarının %10-65 arasında bulunduğu, asidik (felsic) bileşimli, derinlik (plutonic, intrusive) kayacıdır. (Erkan, 2006)
Granit’in kimyasal içeriğinin ortalama değeri, dünya genelinde yapılan, 2485 çözümlemeye[1] göre SiO2 (% 72.04), Al2O3 (% 14.42), K2O (% 4.12), Na2O (% 3.69%), CaO (% 1.82), FeO (% 1.68), Fe2O3 (% 1.22), MgO (% 0.71), TiO2 (% 0.30), P2O5 (% 0.12), MnO (% 0.05) bulunmuştur. (Wikipedia, 2008)
Makrsokobik yani mikroskop kullanmadan gözle görülebilen granit, genellikle yarı özşekilli ve özşekilsiz tanesel dokuya sahip kristalli bir kayaçtır. Ama fenokristallerin barındığı, porfirik dokuyada sahip olabilirler. ( bkz. Şekil 1) Pembe alkali feldispatlar (mikroklin, ortoklaz, sanidin); renksiz kuvars; beyaz plajiyoklaz; siyah biyotit (bazen beyaz muskovit) içeriğine sahiptir. (bkz. Şekil 1,2) Tabi ki bu ana mineraller dışında tali (ikincil) minerallerde içerebilir. Örneğin hematit, rutil gibi.

Şekil 1. Granite (porphyritic); Shap, Cumbria, NW England. In terms of its mineral content this is a typical granite, consisting of pink potassium feldspar, cream sodium feldspar (plagioclase), grey quartz and black biotite mica. The most striking feature of its texture is the large pink angular potassium feldspar crystals (one of which is indicated by the yellow pointer). This texture, of large well-formed crystals in a finer matrix, is called porphyritic. It indicates that some crystals formed early in the magma, and had quite a long time to grow large before the magma was brought into the place where it finally cooled and crystallized. Porphyritic texture is quite common in granites, as well as in lavas erupted from volcanoes. (OESIS, 2008)

Şekil 2. Granite; Loch Laxford, NW Scotland. This cut surface of a hand specimen shows the typical minerals of a granite. There are two varieties of feldspar: potassium feldspar is pink in colour, sodium feldspar is white. Quartz is glassy and transparent, appearing grey in hand specimen. These three minerals make up more than 95% of the rock Small amounts of black minerals are present: these are magnetite (iron oxide) and biotite (dark mica). The texture 8consists of interlocking crystals up to 1 cm across. Although in many granites the larger feldspars may show regular blocky shapes, in this one they are mostly more rounded. (OESIS, 2008)
Mikroskobik yani mikroskop aracılığıyla görülebilen granit’in, birinci nikol görüntüsünde feldispat (K ve zengin Na) ve kuvars baskın ve az miktardaki koyu renkli mineralleri görebiliyoruz. (bkz. şekil 3) İkinci nikol görüntüsünde ise muskovit varlığı ve ikincil mineral turmalin de ortaya çıkıyor. (bkz. Şekil 4)

Şekil 3. Granites are coarse-grained intrusive igneous rocks made of two different kinds of feldspar (potassium- and sodium-rich), together with quartz and a small proportion of dark minerals. In this view of a granite from Cornwall, the feldspars have a dusty appearance, and the quartz is clear. The only “dark” mineral is a small amount of yellow tourmaline (right). Field of view 8 mm. (OESIS, 2004)

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