Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction, whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons.
Therefore, granitic rocks form the basement of all land continents.
Granite has a slow cooling process which forms larger crystals.
The letter-based Chappell & White classification system was proposed initially to divide granites into I-type granite (or igneous protolith) granite and S-type or sedimentary protolith granite.
Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history as a construction stone.
The average density of granite is between 2.65 and 2.75 g/cm Granite is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar on the A-Q-P half of the diagram.
When a granitoid contains less than 10% orthoclase, it is called tonalite; pyroxene and amphibole are common in tonalite.
A granite containing both muscovite and biotite micas is called a binary or two-mica granite.
For instance, a granite that is formed from melted sediments may have more alkali feldspar, whereas a granite derived from melted basalt may be richer in plagioclase feldspar.
It is on this basis that the modern "alphabet" classification schemes are based.
Granitoids have crystallized from magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve).
Magmas will evolve to the eutectic because of igneous differentiation, or because they represent low degrees of partial melting.
Fractional crystallisation serves to reduce a melt in iron, magnesium, titanium, calcium and sodium, and enrich the melt in potassium and silicon – alkali feldspar (rich in potassium) and quartz (Si O), are two of the defining constituents of granite.