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In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. [ 1] It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen ...
The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class. [9] Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava.
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.
Gneiss ( / naɪs / nice) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss is formed under pressures anywhere from 2 to 15 kbar, sometimes even more, and temperatures over 300°C (572°F).
Color index is a geological term, an indicator of the types of minerals present, and the specific type of rock. The color index of an igneous rock is a measure of the ratio of dark colored, or mafic, minerals to light colored, or felsic, minerals. [1] Speaking broadly, mineral colour points out the specific gravity of the mineral, as minerals ...
Obsidian is mineral -like, but not a true mineral because, as a glass, it is not crystalline; in addition, its composition is too variable to be classified as a mineral. It is sometimes classified as a mineraloid. [ 20] Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic.
Tholeiitic magma series. The tholeiitic magma series ( / ˌθoʊliˈaɪtɪk /) is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member.
Felsite is a very fine-grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green ...