Is pegmatite mafic or felsic?
Is pegmatite mafic or felsic?
Pegmatites are little different from the common igneous rocks in major elements of bulk composition, and they range from felsic to mafic (silica-rich to silica-poor); granitic and syenitic types are most abundant.
Is peridotite a felsic?
Compilations of many rock analyses show that rhyolite and granite are felsic, with an average silica content of about 72 percent; syenite, diorite, and monzonite are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is …
What kind of rock is pegmatite?
intrusive igneous rocks
Pegmatites. Pegmatites are intrusive igneous rocks. They produce a greater range of gemstones than any other rock type and have also been the source of some of the largest gemstones ever mined.
Is pegmatite volcanic or plutonic?
In the modern usage, pegmatite describes any plutonic igneous rock consisting almost entirely of crystals at least a centimeter in diameter. While most pegmatite does consist of granite, the rock is defined by its structure, not its composition, and.
What is felsic lava?
Felsic lavas are low temperature lavas because lower temperatures are required to keep felsic minerals molten (and if it was hotter it would have incorporated more iron and magnesium in comparison to silica). So, mafic lavas are hot , low in silica and volatiles, and have relatively low viscosity.
Why is pegmatite coarse-grained?
They are coarse-grained because of high volatile content which makes the magma less viscous and therefore enhances mineral growth (chemical elements are free to move to look for and join a suitable and already existing crystal).
Is peridotite sedimentary or metamorphic?
Layered peridotites are igneous sediments and form by mechanical accumulation of dense olivine crystals. Some peridotite forms by precipitation and collection of cumulate olivine and pyroxene from mantle-derived magmas, such as those of basalt composition.
How does a pegmatite form?
Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith. Pegmatite can also form in fractures that develop on the margins of the batholith. This is how pegmatite dikes are formed.
What is the difference between mafic and felsic lava?
Mafic magmas are low in silica and contain more dark, magnesium and iron rich mafic minerals, such as olivine and pyroxene. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar. The higher the amount of silica in the magma, the higher is its viscosity.
How is felsic magma formed?
It has been suggested that felsic magmas found at subduction-zone volcanoes are produced by mechanisms including fractional crystallization with or without crustal assimilation8, partial melting of the crust9,10, and partial melting of metasomatised silica-excess pyroxenite mantle11,12.
What kind of magmatic rock is pegmatite?
Silica undersaturated (without quartz) magmatic rocks may be also pegmatitic. The term “pegmatite” was first used by a French mineralogist René Haüy, but he used this term as a synonym of graphic granite.
What kind of rocks are mafic in composition?
The magma is very MAFIC in composition. MAFIC IGNEOUS ROCKS include: GABBRO – phaneritic (large crystals) of mafic minerals: olivine, pyroxene, etc. BASALT – aphanitic (small crystals) of mafic minerals: olivene, pyroxene, etc. Mafic rocks (basalt and gabbro) are very dark in color and very dense because of their high iron content.
How does a pegmatite form in a batholith?
Pegmatite. They form small marginal parts of large magma intrusions known as batholiths. They form as a late-stage magmatic fluid starts to crystallize. This fluid is rich in water, other volatiles, and chemical elements incompatible in main magmatic minerals.
What kind of minerals are found in felsic rocks?
Most Common Minerals Rock Name felsic may contain a few minerals typical of felsic rocks rhyolitic tuff medium may contain a few minerals typical of intermediate rocks andesitic tuff mafic may contain a few minerals typical of mafic rocks basaltic tuff