Pegmatites yield precious gemstones, rare minerals, and useful dimension stones & stone aggregates for the construction industry. World of Stones USA is going to introduce you to the untouched or lesser explored rock type on the web and brought public awareness for it.

Well, World of Stones USA is a natural stone supplier mainly for the dimension stone industry. So, why should it take an interest in the discussion on pegmatites like gem industry rocks? 

It is because all pegmatite mines are not yielding only gemstones or precious minerals for the different industries. It also yields the rocks that have values in construction and dimension stone industries, after careful mining around the globe. 

Let’s check some facts, properties, and uses of pegmatites rocks at a glance in the current post.

By definition, Pegmatite rock is holocrystalline and composed of interlocking phaneritic crystals. However, Pegmatite is a known name in the gemstone industry rather than the construction or dimension stone industry. According to Wikipedia, Pegmatites are Extreme Igneous Rocks. Here, extremity means more than one thing. What Is Pegmatite?

It is the final stage of the crystallization of the magma.

  • It indicates that it is the slowest cooling and crystallization process.
  • It contains comparatively larger crystals with rare mineral content.
  • Pegmatites usually contain precious gemstones varieties such as topaz, emerald, and aquamarine gems.

The term “Pegmatite” was first used by a French mineralogist René Haüy for “Graphic Granites” like rocks.

How Does Pegmatite Form?

For the sake of comprehension, we can segregate the formation process of pegmatite in the following steps.

  • We know magma is a hot suspension of the earth, making fundamental elements. In simple words, it is suspended mineral grains and dissolved gases. 
  • Due to atomic and volatile activities, magma gets a high temperature, and subsequently, fluidity increasing in melted magma. Hence, the pressure in the mantle or crust of the earth.
  • Due to pressure, magma finds its way out to the top of the surface through blasts, quakes, fissures, and existing volcanic vents.
  • The erupted magma is now known as Volcanic Lava, and that goes to the cooling process; hence, crystallization of various minerals takes place.
  • Some Magma comes out on the surface of the earth while some remain beneath the ground or crust of the earth.
  • The entire process forms different types of igneous rocks.

The most interesting thing during the igneous rock formation is the speed of cooling and crystallization of various minerals existing in the magma as well as in the surrounding substances/rocks/stuff of the earth.

  • In normal conditions, the lava cools and mineral grain formation happens. The crystallization of mineral grains forms the igneous rocks. 
  • When instantaneous cooling of lava takes place, so, mineral grains formation cannot take place and result directly into the glass formation. 
  • When delayed cooling of magma, particularly (more than 5 Km) deep areas of the underground surface of the earth, takes place, the resulting crystallization yields granites and pegmatite deposits.

However, pegmatite formation is highly complex and takes place in a unique way & conditions. Let’s see how it is.

  • We know magma is a complex suspension. It also contains granitic substances with dissolved water. 
  • During the slow cooling process under the ground/crust, anhydrous mineralization of feldspar like granitic content takes place. 
  • It leaves water-rich residue behind. Some rare chemical elements such as beryllium, lithium, and niobium found in the water-rich residue.
  • Due to the chemical nature, these rare residues are hardly entering into the atomic substitution in the granite minerals, including feldspar, quartz, and mica in normal conditions.
  • However, in the water-rich residue of magma, these rare elements migrate to the peripheral regions of the main granite mass in the rock.
  • Now, the water-rich residue of magma completely cools and crystallizes to form small bodies. These are Pegmatites.  

Mineral Composition of Pegmatites

Mineral content  Apatite, Beryl, Feldspar, Fluorite, Garnet, Lepidolite, Quartz, Silica, Spodumene, Topaz
Compound content  Aluminum Oxide, CaO, Iron(III) Oxide, FeO, Potassium Oxide, Magnesium Carbonate, MgO, & Phosphorus Pentoxide.

Properties of Pegmatites Stones

Parameter  Values 
Hardness 7
Grains Medium to coarse
Fracture Conchoidal
Streak White 
Porosity Less porous
Luster Vitreous, grainy, and pearly 
Compressive strength 178.54 N/mm2
Density 2.6 to 2.65 g/cm2
Toughness 2.1
Specific gravity 2.6-2.63
Cleavage Perfect 
Transparency Translucent to opaque 
Color Black, brown, cream, green, grey, pink, red, rust, silver, white, and yellow.
Resistance Heat, pressure, impact, water, scratch, stain, acid, and wind.

Occurrence of Pegmatites

Do you know pegmatites occur across the planet and found in almost all continents? For example,

Continent  Countries/regions
Asia: India, Iran, Japan, Nepal, China, Russia, Saudi Arabia, North Korea, and South Korea.
Africa: South Africa.
Europe: Ireland, Italy, Netherlands, France, Spain, Greece, Austria, Slovakia, Turkey, and Ukraine.
America: Canada & Brazil.
Oceania: Australian Peninsulas, including New South Wales, Queensland, South Australia, & Western Australia.

Uses of Pegmatites

Commercial Uses of Pegmatites:

Pegmatite Rock - Uses, Facts & Properties

The commercial significance of pegmatites is its rare elements/mineral constituents.

  • Beryl-an ore of Beryllium
  • Spodumene-an ore of Lithium
  • Niobium
  • Tantalum
  • Cesium
  • Sheet Mica
  • Tourmalines
  • The gem forms of Beryl like Aquamarine, Topaz, and Emerald

Types of Pegmatites 

When changes of the main mineral content found, the industrial names of the pegmatites are changing accordingly. 

For instance, when pegmatites have a mineral composition similar to the Granites, such as the predominance of quartz, feldspar, and mica, they usually term as Granite Pegmatites.

When the dominance of one of the Common Minerals in Granite Pegmatite takes place, the look-n-feel of the rocks changes accordingly.

  • Quartz 
  • Muscovite 
  • Plagioclase with Oligoclase Composition 
  • Microcline 

Similarly, the following types of pegmatites known in the stone industry.

  • Spessartine Pegmatite
  • Gabbroic Pegmatite
  • Tourmaline Pegmatite
  • Tonalite Pegmatite

Commercial Applications of Pegmatites:

The most important thing in pegmatite is the presence of an adequate amount of Rare Earth Elements (REE), which are in high demand in various modern applications, including

  • The consumer electronics products.
  • The automobile Catalytic Converters and Rechargeable Batteries.

The uses of main REEs found in pegmatites are:

REE Uses
Apatite: It is the main source of phosphorous-containing minerals and biological minerals used in Agriculture, Pharmaceutical, and chemical industries.
Tantalum:  By property, Tantalum is very hard, extremely corrosion-resistant, easily fabricated, and is a good conductor of heat and electricity. Therefore, 

  • It is useful in high-end product manufacturing, such as mobile phones, DVD players, video cameras, personal computers, video game systems, and televisions.
  • In the aircraft industry, it is useful in alloys making for jet engine components. 
  • It is using in metalworking tools making, chemical process equipment, nuclear reactors, and missile parts.
  • It also uses in products like camera lenses, surgical instruments, and implants.
Lithium:  Lithium-ion (Li-ion) batteries have become the energy storage solution of choice 

  • For portable electronic devices such as laptops and smartphones. 
  • For electric and hybrid vehicles with new battery technologies.

Uses of Pegmatites in the Gemstone Industry:

Rare minerals mean, the pegmatites are essential components in creating artwork, jewelry, source of corundum, tourmalines, beryl, and topaz.

  • Creating artwork
  • Jewelry
  • Source of corundum
  • Tourmalines
  • Beryl
  • Topaz

Uses of Pegmatites in the Construction Industry:

Pegmatite rocks are a great source of construction aggregates, road aggregates, and as a base material in landscaping & outdoor paving in nearby areas of pegmatite quarries or mines.

Architectural Uses of Pegmatites in Dimension Industry:

Due to stunning appearance and mineral values, pegmatites are high-quality decorative aggregates.

Besides these, the applications of pegmatites are known as the building stones, facing stones, and paving stones

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