Chiuveta granit online dating
Granite often occurs as relatively small, less than 100 km² stock masses (stocks) and in batholiths that are often associated with orogenic mountain ranges.
A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: Much of it was intruded during the Precambrian age; it is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the 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.The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock.Strictly speaking, granite is an igneous rock with between 20% and 60% quartz by volume, and at least 35% of the total feldspar consisting of alkali feldspar, although commonly the term "granite" is used to refer to a wider range of coarse grained igneous rocks containing quartz and feldspar.The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin.
These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals.
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.
This process operates regardless of the origin of the parental magma to the granite, and regardless of its chemistry.
Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic.
A granitic rock with a porphyritic texture is known as a granite porphyry.
When a granitoid contains less than 10% orthoclase, it is called tonalite; pyroxene and amphibole are common in tonalite.