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According to the Encyclopædia Britannica, color indices, 0–50 are felsic, 50–90 are mafic, and 90–100 are ultramafic. [6] An online geology textbook provides an example of the use of another classification scheme, in which color indices 0–15 are felsic, 15–45 are intermediate, 45–85 are mafic, and 85–100 are ultramafic. [9]
Felsic magmas and lavas have lower temperatures of melting and solidification than mafic magmas and lavas. Felsic rocks are usually light in color and have specific gravities less than 3. The most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars (albite-rich).
Alkali feldspar granite, some varieties of which are called 'red granite', [1] is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals. [2] [3]
Mafic enclave in granite rock, at Yosemite National Park Granite forms from silica-rich ( felsic ) magmas. Felsic magmas are thought to form by addition of heat or water vapor to rock of the lower crust , rather than by decompression of mantle rock, as is the case with basaltic magmas. [ 19 ]
They are characteristically felsic. The feldspar component of syenogranite is predominantly alkaline in character (usually orthoclase ). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20% plagioclase , 15–20% quartz , 5–8% biotite , 3–5% hornblende , and ...
In a simplified compositional classification, igneous rock types are categorized into felsic or mafic based on the abundance of silicate minerals in the Bowen's Series. Rocks dominated by quartz, plagioclase, alkali feldspar and muscovite are felsic. Mafic rocks are primarily composed of biotite, hornblende, pyroxene and olivine.
Experts explain whether ice or heat for back pain will lead to better relief, and the best time to use each. ... a good rule of thumb is to pick either cold or heat and trial for 20 minutes to see ...
The mafic minerals in the TTG rock body, possibly biotite, were weathered, which introduced a brownish coating on the TTG rock surface. Tonalite–trondhjemite–granodiorite ( TTG ) rocks are intrusive rocks with typical granitic composition ( quartz and feldspar ) but containing only a small portion of potassium feldspar .