Full Answer
Is pegmatite a good stone for architecture?
However, pegmatite deposits often contain gemstones, industrial minerals, and rare minerals. Pegmatite rock has limited use as an architectural stone. Occasionally it is encountered in a dimension stone quarry that produces granite for architectural use.
What is the composition of a pegmatite?
To be called a “pegmatite,” a rock should be composed almost entirely of crystals that are at least one centimeter in diameter. The name “pegmatite” has nothing to do with the mineral composition of the rock. Most pegmatites have a composition that is similar to granite with abundant quartz, feldspar, and mica.
How rare is a pegmatite?
While pegmatite occurrences are not uncommon, those bearing gem-quality minerals in mineable quantities are exceedingly rare. The most widely accepted model of pegmatites formation is “fractional crystallization”.
How do you identify pegmatite?
Hence, pegmatite is often characterised by sampling the individual minerals that compose the pegmatite, and comparisons are made according to mineral chemistry. A common error is to assume that the wall zone is a chilled margin whose composition is representative of the original melt.
Is pegmatite rock valuable?
Rare elements concentrated in large crystals make pegmatite a potential source of valuable ore. Rare earth elements are so named not because they are actually rare but because they are usually found within other minerals, which makes them difficult and costly to mine.
Why are pegmatites so important?
Economic importance Pegmatites are important because they often contain rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin, rare earth, and tungsten minerals, among others.
What is pegmatite mostly used for?
Pegmatite is frequently mined for industrial minerals. Large sheets of mica are mined from pegmatite. These are used to make components for electronic devices, retardation plates, circuit boards, optical filters, detector windows, and many other products. Feldspar is another mineral frequently mined from pegmatite.
Is gold found in pegmatite?
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.
Why is pegmatite an economically important igneous rock?
Granite pegmatite typically contains feldspar, mica, and quartz. Pegmatite is an economically-important rock because it is the source material for lithium, cesium, and rare earth elements and because it may hold large gemstones.
What minerals are found in pegmatite?
Quartz and alkali feldspars are the essential constituents; the most common varietal and accessory minerals are muscovite, biotite, apatite, garnet, and tourmaline. Many granitic pegmatites contain unusual concentrations of the less-abundant elements.
Where is pegmatite mined?
Harding Pegmatite MineThe Harding Pegmatite Mine is a former beryl quarry in New Mexico.LocationHarding MineLocationPicuris MountainsStateNew Mexico11 more rows
How is pegmatite mined?
Because these dikes and pockets are small in size, the mining operations that exploit them are also small. The mining of pegmatites might be done in an underground operation that follows a dike or exploits a small pocket.
How do you get crystals out of pegmatite?
2:0815:22Found Quartz Crystals While Prospecting For Pegmatite - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd it's very common all common to find quartz crystals as well as other minerals because it allowedMoreAnd it's very common all common to find quartz crystals as well as other minerals because it allowed the crystals to grow large because it cooled slowly over time alright.
What is a pegmatite deposit?
Pegmatite deposits Certain magmas, such as those which form granites, contain several percent water dissolved in them. When a granitic magma cools, the first minerals to crystallize tend to be anhydrous (e.g., feldspar), so an increasingly water-rich residue remains.
Why do most gems come from pegmatites?
The high water content of the magma makes it possible for the crystals to grow quickly, so pegmatite crystals are often large.
How do you identify pegmatites?
0:071:22Identifying Pegmatite - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd the pegmatite refers to the. As you can see there's a large potassium feldspar crystal a singleMoreAnd the pegmatite refers to the. As you can see there's a large potassium feldspar crystal a single crystal that comes through here and it's integral in this area with a large quartz crystal.
Why are pegmatite crystals so big?
The ions in the water are much more mobile than ions in the melt. This allows them to move about freely and form crystals rapidly. This is why crystals of a pegmatite grow so large. The extreme conditions of crystallization sometimes produce crystals that are several meters in length and weigh over one ton.
What are LCT pegmatites?
Lithium-cesium-tantalum (LCT) pegmatites comprise a compositionally defined subset of granitic pegmatites. The major minerals are quartz, potassium feldspar, albite, and muscovite; typical accessory minerals include biotite, garnet, tourmaline, and apatite.
Does pegmatite cool slow or fast?
Pegmatites do form where magmas cool relatively slowly within the earth compared to the fast cooling they would experience if they had erupted on to the earths surface. But pegmatites are associated both in time and space with other igneous rocks that formed at the same depth and show much smaller grains.
What does a porphyritic texture indicate about the cooling history of an igneous rock?
What does a porphyritic texture indicate about the cooling history of an igneous rock? It indicates that crystals were formed at depth (slow cooling) and then the magma moved to a shallow depth or erupted (fast cooling).
What is pegmatite mineral?
Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, and somewhat with skarn associated mineralisation.
How big is a pegmatite body?
Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies. Pegmatite body size is on the order of magnitude of one to a few hundred meters. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages.
What is lithian pegmatite?
Pegmatites can be classified according to the elements or mineral of interest, for instance " lithian pegmatite" to describe a Li-bearing or Li-mineral bearing pegmatite, or " boron pegmatite" for those containing tourmaline .
What is the mineralogy of pegmatite?
Note pink potassium feldspars and cumulate-filled chamber. The mineralogy of a pegmatite is in most cases dominated by some form of feldspar, often with mica and usually with quartz, being altogether "granitic" in character.
What is the product of pegmatite decomposition?
Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye. The product of pegmatite decomposition is euclase . Proterozoic pegmatite swarm in the headwall of the cirque of a small mountain glacier, northeastern Baffin Island, Nunavut.
What is the name of the crystals that make up pegmatite?
The word pegmatite derives from Homeric Greek, πήγνυμι ( pegnymi ), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite. Most pegmatites are composed of quartz, feldspar , and mica, having a similar silicic composition as granite.
What is the name of the rock that has corundum crystals?
Pegmatite with blue corundum crystals. Pegmatite containing lepidolite, tourmaline, and quartz from the White Elephant Mine in the Black Hills, South Dakota. A pegmatite is an igneous rock, formed by slow crystallization at high temperature and pressure at depth, and exhibiting large interlocking crystals usually greater in size than 25 mm ...
What is a pegmatite specimen?
To some of us, pegmatites are the most captivating of all igneous rocks. In the absolute sense, they are an exceptionally coarse-grained intrusive igneous rock ...
What is the shape of a pegmatite?
The shape of pegmatite bodies range from from tabular to inverted teardrop-shaped and range in size from several tens of meters up to a kilometer or more in extent!
What are some gems that are miarolitic pegmatites?
Check out the main iRocks website and its mineral galleries! These miarolitic pegmatites are a rich source of gemstones such as aquamarine, morganite, heliodor, rubellite, indicolite, "liddicoatite", kunzite, topaz, brazilianite, spessartine, chrysoberyl, and fluorapatite.
What are the elements in granite pegmatites?
These include cesium, rubidium, lithium, beryllium, tantalum, niobium, tin, boron, and zirconium, along with a few others. ...
Which countries have pegmatites?
Countries containing renown pegmatites include Brazil, Mozambique, Pakistan, Afghanistan, USA (California, Colorado, South Dakota, and the New England area), Madagascar, Burma, Canada, Italy, South Africa, Norway, Russia, and Germany. Given the number of pegmatites you'll discover on the internet, you might begin to view them as abundant – however, ...
What percentage of magma is beryl rich?
According to Dr. David London, beryl-rich rare-element pegmatites constitute 0.003 percent of the entire magma body. Tourmalines and spodumenes reflect similar concentration percentages for boron and lithium.
What is the composition of pegmatites?
Pegmatite Formation. Geologically, pegmatites can be defined as very coarse- to gigantic-sized (tens of meters) igneous rocks of commonly granitic (high silica, low magnesium) with minor gabbroic or even ultramafic (low silica, high magnesium) composition. However, gem deposits refer only to those of granitic composition.
Where are pegmatites found?
More than 70 colored minerals are extracted from these bodies, including emerald (green, Cr or Cr–V bearing beryl), alexandrite (a variety of chrysoberyl), aquamarine, heliodor, morganite (blue, yellow and pink varieties of beryl correspondingly), topaz, spessartine, spodumene indicolite, rubellite, verdelite and liddicoatite (blue, red, green and light-brown varieties of tourmaline). Typically, all of these minerals are found within miarolitic cavities (gem-bearing pockets) in the core of pegmatitic body. The most distinguishing feature of pegmatites is the presence of extremely large sized crystals (e.g. gem-quality beryl measuring 55 x 18 x 16 cm in size and weighting 22 kg was extracted from Volyn pegmatite field, Ukraine). Additionally, pegmatites are also known to be a significant source of rare elements, such as Be, Nb, Ta, Sn, Li, Rb and Cs. This article will review the generally accepted model of the pegmatite formation and shed light into the geology of Volyn pegmatite deposit, Ukraine – one of the greatest sources of gem minerals in Europe.
What are the minerals in a pegmatite pocket?
The pockets typically contain crystals of morion (a dark brown to black variety of smokey quartz), beryl, topaz and are filled with fine detrital quartz and clay-micaceous matrix. The crystals are often very impressive – morions weighing more than 1000 kg, beryls up to 22 kg, topazes up to 117 kg. The other minerals found in these pegmatites are ...
How do pegmatites crystallize?
Pegmatites crystallize inwards from their contacts with country rocks. The idealized scheme is (from outer parts of pegmatitic body to the core) as follows: 1 Border zone of fine-grained granite 2 Wall zone represented by coarser granite or “graphic granite” (quartz + K-feldspar intergrowth) 3 Outer (Intermediate zone) is progressively coarser to giant size crystals (blocky K-feldspar + development of pockets) 4 Core margin (inner intermediate) zone (giant crystals development + gem quality crystals of tourmaline, topaz and beryl) 5 Core zone, which consist of massive quartz
How much does a blue topaz cost?
Clear cut blue topazes price range from $10 to $100 per carat, depending on color, clarity and cut of stone. Beryl at the Munich Show. Volyn pegmatite deposit, Ukraine.
How much does a carat of Volyn beryl cost?
The samples with these surfaces are highly valued and much desired in mineral collections. One carat of faceted Volyn beryl typically sells for $80.00.
What are the rare elements found in pegmatites?
Additionally, pegmatites are also known to be a significant source of rare elements, such as Be, Nb, Ta, Sn, Li, Rb and Cs. This article will review the generally accepted model of the pegmatite formation and shed light into the geology of Volyn pegmatite deposit, Ukraine – one of the greatest sources of gem minerals in Europe.
Formation
- Pegmatites are extreme igneous rocks that form during the final stage of a magmas crystallization. They are extreme because they contain exceptionally large crystals and they sometimes contain minerals that are rarely found in other types of rocks. Pegmatites form from …
Composition
- To be called a pegmatite, a rock should be composed almost entirely of crystals that are at least one centimeter in diameter. The name pegmatite has nothing to do with the mineral composition of the rock. Most pegmatites have a composition that is similar to granite with abundant quartz, feldspar, and mica. These are sometimes called granite pegmatites to indicate their mineralogic…
Properties
- These pockets of superheated water are extremely rich in dissolved ions. The ions in the water are much more mobile than ions in the melt. This allows them to move about freely and form crystals rapidly. This is why crystals of a pegmatite grow so large. The extreme conditions of crystallization sometimes produce crystals that are several meters in length and weigh over one …
Usage
- Because these dikes and pockets are small in size, the mining operations that exploit them are also small. The mining of pegmatites might be done in an underground operation that follows a dike or exploits a small pocket. It can also be done at an outcrop where the pegmatite is easily discovered by people. Pegmatites usually do not support large mining operations that employ d…
Geology
- Some of the worlds best gemstone mines are in pegmatites. Gemstones found in pegmatite include: amazonite, apatite, aquamarine, beryl, chrysoberyl, emerald, garnet, kunzite, lepidolite, spodumene, topaz, tourmaline, zircon, and many others. Large crystals of excellent-quality material are often found in pegmatite. Pegmatite is the host rock for many rare mineral deposits…
Applications
- Pegmatite is often mined for industrial minerals. Large sheets of mica are mined from pegmatite. These are used to make components for electronic devices, retardation plates, circuit boards, optical filters, detector windows, and many other products. Feldspar is another mineral frequently mined from pegmatite. It is used as a primary ingredient for making glass and ceramics. It is als…
Overview
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer intermediate composition and mafic pegmatites are known.
Etymology
The word pegmatite derives from Homeric Greek, πήγνυμι (pēgnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite. The term was first used by René Just Haüy in 1822 as a synonym for graphic granite. Wilhelm Karl Ritter von Haidinger first used the term in its present meaning in 1845.
General description
Pegmatites are exceptionally coarse-grained igneous rocks composed of interlocking crystals, with individual crystals usually over 1 centimeter (0.4 in) in size and sometimes exceeding 1 meter (3 ft). Most pegmatites have a composition similar to granite, so that their most common minerals are quartz, feldspar, and mica. However, other pegmatite compositions are known, including compositions similar to nepheline syenite or gabbro. The term pegmatite is thus purely a textural d…
Petrology
Pegmatites form under conditions in which the rate of new crystal nucleation is much less than the rate of crystal growth. In other words, molecules in the fluid from which the crystals are growing are much more likely to join an existing crystal than to come together to start a new crystal. This favors growth of a few very large crystals. In normal igneous rocks, coarse texture is a result of slow cooling deep underground. However, the extraordinarily coarse texture of pegmatites must …
Mineralogy
Most pegmatites have a simple composition, often being composed entirely of minerals common in granite, such as feldspar, mica, and quartz. The feldspar and quartz often show graphic texture. Rarely, pegmatites are extremely enriched in incompatible elements, such as lithium, caesium, beryllium, tin, niobium, zirconium, uranium, thorium, boron, phosphorus, and fluorine. These complex …
Geochemistry
Pegmatites are enriched in volatile and incompatible elements, consistent with their likely origin as the final melt fraction of a crystallizing body of magma. However, it is difficult to get a representative composition of a pegmatite, due to the large size of the constituent mineral crystals. Hence, pegmatite is often characterised by sampling the individual minerals that compose the pegmatite…
Economic importance
Pegmatites are important because they often contain rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin, rare earth, and tungsten minerals, among others.
Pegmatites are the primary source of lithium either as spodumene, lithiophyllite or usually from lepidolite. The primary source for caesium is pollucite, a mineral fr…
Occurrence
Notable pegmatite occurrences are found worldwide within the major cratons, and within greenschist-facies metamorphic belts. However, pegmatite localities are only well recorded when economic mineralisation is found.
Pegmatites are found as irregular dikes, sills, or veins, and are most common at the margins of batholiths (great masses of intrusive igneous rock). Most are cl…