Pegmatite is an exceptionally coarse-grained plutonic igneous rock. Most pegmatites have a mineralogical composition of granite but composition has no defining importance here. Pegmatites may have any imaginative magmatic composition and they are actually known to contain a large number of unusual minerals.
Is spodumene an igneous rock?
Pegmatite is a coarse-grained igneous rock that crystallized deep inside the crust from the late magmatic liquid that contained lots of chemical elements that didn’t fit into the crystal structure of common minerals. Hence, pegmatites often contain rare minerals (spodumene, tourmaline, beryl, lepidolite, etc.)
How do pegmatites 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 are pegmatites quizlet?
define pegmatite. – intrusive igneous rocks with very coarse to gigantic texture. – best rock type for finding high quality gemstones. – have composition similar to granite, but significantly enriched in rare elements.
Where are pegmatites found?
Pegmatites: How to Locate a New Mineral Rich Locality.
Is Phaneritic intrusive or extrusive?
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth’s surface.
Is pegmatite felsic or mafic or intermediate?
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 Obsidian mafic or felsic?
It is sometimes classified as a mineraloid. Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic.
What is the difference between granite and pegmatite?
Pegmatite is chemically identical to granite, but has a much coarser crystal structure. Common colors are gray, white, and pink. Pegmatite is quarried for decorative stone and as a source of beryllium, columbium and tantalum when these are present.
What is a Phenocrysts in geology?
A relatively large crystal embedded in a finer-grained or glassy igneous rock. The presence of phenocrysts gives the rock a porphyritic texture (see illustration). Phenocrysts are represented most commonly by feldspar, quartz, biotite, hornblende, pyroxene and olivine.
What type of rock is gneiss?
gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale. Gneiss usually is distinguished from schist by its foliation and schistosity; gneiss displays a well-developed foliation and a poorly developed schistosity and cleavage.
What type of rock is pumice?
Pumice is pyroclastic igneous rock that was almost completely liquid at the moment of effusion and was so rapidly cooled that there was no time for it to crystallize. When it solidified, the vapours dissolved in it were suddenly released, the whole mass swelling up into a froth that immediately consolidated.
What is the meaning of Phaneritic?
Of or relating to an igneous rock in which the crystals are so coarse that individual minerals can be distinguished with the naked eye. Phaneritic rocks are intrusive rocks that cooled slowly enough to allow significant crystal growth. Compare aphanitic.
What are pegmatites choice answer choices?
Pegmatites are extreme igneous rocks that form during the final stage of a magma’s crystallization. They are extreme because they contain exceptionally large crystals and they sometimes contain minerals that are rarely found in other types of rocks.
Why do geologists make thin sections?
Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin and evolution of the parent rock.
Why do geologists make thin sections quizlet?
Why do geologists make thin sections? To observe the shapes of mineral grains. What are the differences in how an intrusive igneous rock and an extrusive igneous rock form? Intrusive igneous rock cools slowly beneath Earth’s surface, while extrusive igneous rock cools rapidly at or near Earth’s surface.
Are pegmatites plutonic?
PEGMATITE is a common plutonic rock, of variable texture and coarseness, that is composed of interlocking crystals of widely different sizes. The most spectacular pegmatites contain abnormally large crystals mixed with medium sized and smaller crystals. Crystals up to many meters long have been reported.
What special component of magma allows pegmatites to form?
Crystals of pegmatite grow large because of the extreme conditions of crystallization. Basically, the presence of residual water has allowed the magma to cool slowly to permit coarse crystal growth. Complex pegmatites result because of the presence exotic volatiles such as chlorine, fluorine, and carbon dioxide.
What are pegmatitic textures?
A pegmatitic texture is one in which the mineral grains are exceptionally large. The largest ones are, by convention, more than about 3 cm long. This texture is found in intrusive rocks. … Instead, the large crystals of a pegmatite formed in a magma that was extra rich in dissolved water.
What is calcite mineral used for?
Calcite is the mineral component of limestone which is used primarily as construction aggregates, and in production of lime and cement.
Is spodumene a silicate mineral?
Spodumene is a chain silicate/pyroxene-type mineral, with the presence of silica in the tetrahedral form (Skinner and Evans, 1960).