What are the three main minerals found in pegmatite?
Most pegmatites have a composition similar to granite, so that their most common minerals are quartz, feldspar, and mica.
What is tourmaline pegmatite?
Himalaya pegmatite: A specimen of the Himalaya Pegmatite of San Diego County, California, that is famous for yielding gem- and mineral-specimen-quality tourmaline and other fine crystals. This is a pocket piece with feldspar, smoky quartz, cleavelandite, and a fantastic multicolor tourmaline crystal.
What is the composition of pegmatite?
The pegmatite contains 33.6 percent albite, 30.4 percent quartz, 21.0 percent perthite, 14.0 percent muscovite, and 1.0 percent accessory minerals. Its bulk chemical composition is 74.2 per- cent SiO2, 15.0 percent A12Oa, 4.6 percent NarO, 4.2 percent KrO, 0.6 percent HzO, and 1.4 percent other constituents.
What gems are found in pegmatite?
Pegmatites yield huge quantities of tourmaline, beryl (aquamarine and morganite), chrysoberyl, kunzite, and topaz, as well as a host of much rarer gems and minerals. Important descriptions of peg- matites are found in Sinkankas (1981) and Schnei- derhohn (1961). very large crystals and may contain rare minerals.
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 is the chemical composition of tourmaline?
Physical Properties of Tourmaline
| Chemical Classification | Boron silicate |
|---|---|
| Chemical Composition | (Ca,Na,K,[vacancy]) (Li,Mg,Fe+2,Fe+3,Mn+2,Al,Cr+3,V+3)3(Mg,Al,Fe+3,V+3,Cr+3)6 ((Si,Al,B)6O18) (BO3)3(OH,O)3 (OH,F,O) |
| Crystal System | Hexagonal |
| Uses | A popular gemstone and mineral specimen |
Does pegmatite have gold in it?
Gold can occur in economic grades in Pegmatites are magmas containing granitic type minerals (feldspar, quartz, mica) which cool slowly and thus allow for very large crystals (>2.5cm) to form. The gold is deposited through gold bearing sulphides carried by the quartz.
How do you identify phenocrysts?
A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them.
What mineral are phenocrysts?
feldspar minerals
feldspar minerals (A porphyry is an igneous rock containing conspicuous crystals, called phenocrysts, surrounded by a matrix of finer-grained minerals or glass or both.) In most rocks, both alkali and plagioclase feldspars occur as irregularly shaped grains with only a few or no crystal…
Can gold be found in pegmatites?
What minerals are found in tourmaline?
Tourmaline is a trigonal crystalline complex boron silicate mineral composed of aluminum, iron, magnesium, lithium, and potassium with chemical formula (Ca,K,Na)(Al,Fe,Li,Mg,Mn)3 (Al,Cr,Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F), and formed during the pneumatolytic process of igneous rock formation.
What silicate group is tourmaline?
Tourmaline is the name of a large group of boron silicate minerals. These minerals share a common crystal structure and similar physical properties – but vary tremendously in chemical composition.
What is pegmatite texture?
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. The extra large size does not mean that they cooled extra slowly.
Where are phenocrysts found?
Phenocrysts are more often found in the lighter (higher silica) igneous rocks such as felsites and andesites, although they occur throughout the igneous spectrum including in the ultramafics. The largest crystals found in some pegmatites are often phenocrysts being significantly larger than the other minerals.
What are the components of pegmatites?
These pegmatites consist mainly of tourmaline, K-feldspar, quartz, and albite, with accessory zircon ( Fig. 4 i). Black tourmaline (e.g., sample P1-2-3-10) occurs within outer and central granitic units close to the host muscovite granite.
What is tourmaline-bearing granitic pegmatite?
The tourmaline-bearing granitic pegmatite occurs as small irregular bodies and segregations or thin dikes (up to 1 m thick) that commonly have a gradational contact with the host muscovite granite ( Fig. 4 h). Typical pegmatitic textures and parageneses, such as graphic textures and blocky K-feldspar, occur within this unit.
What is a Himalaya pegmatite?
Himalaya pegmatite: A specimen of the Himalaya Pegmatite of San Diego County, California, that is famous for yielding gem- and mineral-specimen-quality tourmaline and other fine crystals. This is a pocket piece with feldspar, smoky quartz, cleavelandite, and a fantastic multicolor tourmaline crystal. Specimen is about 12.7 x 7.7 x 7.5 centimeters.
What is the be content of tourmaline?
The mean Be contents of tourmalines from the two-mica granite, muscovite granite, and granitic pegmatite are 23.2, 28.1, and 38.2 ppm, respectively, which are also higher than the Be contents of tourmalines from the biotite plagiogneiss ( Table A3; Fig. 11 b).