Pegmatite

The pegmatite minerals, pink, grey-white in colour, is an intrusive igneous body of substantially variable grain size. Having an exceptionally large crystal composition may also contain minerals that are not found in other types of rocks. The pegmatite often includes coarse crystal growth and is widely used as a principal ingredient for making glass and ceramics. A pegmatite rock can be segregated within a related plutonic rock or a dike that violates the surrounding country rock. A pegmatite is at least one centimetre in diameter.

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Pegmatite Formation 

Formed during the final stage of magma’s crystallization is pegmatit. It is clearly a pegmatite if it is wholly made of crystals. With pegmatite’s large crystals are accredited to low-viscosity fluids which permit ions to be very mobile. During the stage of crystallization, the melt generally consists of a substantial amount of dissolved water and various other volatiles such as fluorine, chlorine, and carbon dioxide. During the early crystallization process, water is not eliminated, thus its concentration in the melt mushrooms as the crystallization progresses. 

Finally, there is a profusion of water, and pockets of water isolated from the melt. These pockets of highly heated water are superbly rich in dissolved ions. The ions in the water are relatively more mobile than ions in the melt. This enables them to move freely and create crystals quickly. This is why crystals of a pegmatite blossom so large.

The severe conditions of crystallization sometimes form crystals that are some meters in length and weigh over a ton. Pegmatites produce from waters that isolate from magma in the late stages of crystallization; this activity commonly takes place in small pockets beside the margins of a batholith. Pegmatite can also produce fractures that develop along the margins of the batholith. This is also the way the pegmatite dikes are produced.

Pegmatite Composition

The pegmatite mineralogy exercises control from some form of feldspar, frequently with mica and usually with quartz. Pegmatite includes most minerals linked with granite and granite-related hydrothermal systems. However, It is not feasible to measure the mineralogy. This is subjected to the difficulty in counting and sampling mineral grains in a rock that may consist of crystals from centimetres to meters.

Pegmatites involve mafic and carbonate-containing sequences that include garnet, often almandine or spessartine

Syenite pegmatites are depleted of quartz and have huge feldspathoid crystals instead.

Where is Pegmatite Found?

Pegmatite is found all across the world. They are the most copious antiquated rocks, particularly of the great geologic age. Some are found in huge intrusive igneous rocks, while others are spread over rocks enclosing intrusive magmatic rocks.

Properties and Characteristics of Pegmatite Rock

Pegmatites can be characterized in accordance to the elements or mineral of interest, for example, “lithian pegmatite” to define a Li-carrying or Li-mineral carrying pegmatite, or “boron pegmatite” for those having tourmaline.

There is often no rational way to differentiate pegmatites as per the chemistry simply because of the complexity of collecting a representative sample, but often groups of pegmatites can be differentiated on contact textures, accessory minerals, orientation and timing. These can be named either formally or informally as a category of intrusive rock or within a bigger igneous association.

While complex to be certain of extraction of pegmatite in the stringent sense, often pegmatites are termed as “granitic”, “metamorphic”, or “metasomatic”, depending upon the interpretations of the interrogating geologist.

Fun Facts

• Rocks with a texture similar to pegmatites are known as pegmatitic.

• Pegmatite is often traded commercially as a granite product.

• Facts About The Rock

• Crystals of pegmatite grow huge due to critical conditions of crystallization.

• Complex pegmatites come into existence because of the existence of exotic volatiles such as CO₂, chlorine, and fluorine.

• An example of an extremely huge crystal is at the Etta Mine in South Dakota. It was 5 feet in diameter, 42 feet long, and produced about 90 tons of spodumene.

• Pegmatites generally do not support extended mining operations.

• Rare components condensed in huge crystals may make pegmatite a competent source of valuable ore. Pegmatite deposits may also have industrial minerals, rare minerals and gemstones.