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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]
Biotite, sodium-rich amphiboles and pyroxenes along with iron-rich olivine are common minor minerals. Accessory phases include titanite, apatite, corundum, zircon, magnetite and ilmenite. [4] Phonolite's characteristic dark color comes from its concentration of dark pyroxenes such as aegirine and augite. Blairmorite is an analcite-rich variety ...
The series is divided into two branches, the continuous (felsic minerals: feldspars) and the discontinuous (mafic minerals).The minerals at the top of the illustration (given aside) are first to crystallize and so the temperature gradient can be read to be from high to low with the high-temperature minerals being on the top and the low-temperature ones on the bottom.
The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. [3] [4] It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium. [5] [6] [7]
In igneous petrology, an intermediate composition refers to the chemical composition of a rock that has 51.5–63 wt% SiO 2 being an intermediate between felsic and mafic compositions. Typical intermediate rocks include andesite and trachyandesite among volcanic rocks and diorite and granodiorite among plutonic rocks .
Peridotite, a type of ultramafic rock. Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content).
Boninite – Ultramafic extrusive rock high in both magnesium and silica; Carbonatite – Igneous rock with more than 50% carbonate minerals; Charnockite – Type of granite containing orthopyroxene Enderbite – Igneous rock of the charnockite series; Dacite – Volcanic rock intermediate in composition between andesite and rhyolite
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in ...