Lunar Ferroan Anorthosite

Alkali feldspar perthite (7cm long X 3cm width)

feldspars(rus. feldspars , English feldspars; German Feldspate m pl, Feldspte m pl, Feldspat-Familie f, Feld-spatgruppe f ) - A group of the most common rock-forming minerals of the class of silicates of the framework structure, which are characterized by relatively high hardness.

Polevik is the old Ukrainian name for feldspars.

1. General characteristics

Feldspars are approx. 50% mass earth's crust. Approximately 60% of them are contained in igneous rocks ah, in metamorphic - approx. 30%, in sedimentary - 10-11%. Density 2.6-2.8. Op. 6-6.5. According to the chemical composition, these are aluminosilicates of sodium, calcium, potassium, barium, as isomorphic impurities they contain rubidium, lead, strontium, etc.. N.sh. used in glass, paper and other industries, some feldspars as facing material and ornamental stones.

N.S. divided into 3 groups:

Orthoclase - potassium feldspars of composition K 2 O.Al 2 O 3 .6 SiO 2. They occur in the form of crystals, sometimes very large, but mostly in the form of fine-grained masses. Opaque, have a glassy or pearlescent sheen. Complex-sodium feldspars - composition Na 2 O.Al 2 O 3 .6 SiO 2. They occur in the form of fine-grained masses. More transparent than orthoclase. Anorthite-calcium feldspars of composition CaO.Al 2 O 3 .6 SiO 2. They form the same crystals (always small) and crystalline masses as orthoclase and albite.

The plagioclase subgroup is a continuous isomorphic series of albite Na and anorthite Ca. They are characterized by a lamellar structure. Depending on the content of calcium (anorthite) plagioclase molecules are divided into 100 numbers. According to the content of SiO2, they are divided into acidic (No. 0-30), medium (No. 30-50) and basic (No. 50-100). In the subgroup of alkaline s.sh. the most common are orthoclase and microcline. Both minerals have the same composition K and differ only in syngony: orthoclase is monoclinic, and microcline is triclinic syngony. Regular germination of orthoclase or microcline by albite is called perthite, and plagioclase germination by orthoclase or microcline is called antiperthite. Plagioclase includes bytonite, labrador and other minerals. The subgroup of hyalophanes (an isomorphic mixture of K and Ba) is rare and has no practical significance. Of all s.sh. alkaline NL are of the greatest industrial interest. In our country, almost 2/3 of the total production of feldspar raw materials is used in the glass industry and about 1/3 in the ceramic industry.

2. Rocks and ores

Feldspar igneous rocks of a non-pegmatite nature can be divided into two subgroups:

• a) aluminosilicate rocks, consisting mainly of feldspars and quartz - granites, felsites, Aplite, alaskites, etc.;

• b) aluminosilicate rocks, in which there is no quartz, and feldspar is replaced by alkaline minerals - nepheline syenites, miaskites, etc.

Among them are the deposits of alaskitiv in the USA (Spruce Pine), bodies of altered rocks of the granite series (weathering crust) in England, Poland, Japan, and France. One of the classic examples of this subgroup is the Szeblów field in Poland. Greisenized granites from the St. Stephens deposit (Cornwell, England) are also used as feldspar raw materials. This type includes mica granites in Uzbekistan (Lyangarskoe deposit), albitites in Kazakhstan (Mount Aksoran), leucocratic granites in Tajikistan (Takobskoe deposit), muscovite granites in the Urals, granite massifs in Ukraine (Kirovograd region) and others.

The most high-quality feldspar ores for the glass and ceramic industries are coarse-grained and giant-grained feldspar pegmatite veins. Aplite, feldspar sands, altered granites, liparites, felsite-porphyries, etc. are also used in many countries. Abroad, about 2/3 of all feldspar mining is pegmatite raw materials.

3. Deposits

All deposits of feldspar raw materials can be divided into three groups:

• 1. Granite and partially alkaline pegmatites.
• 2. Feldspar igneous rocks of non-pegmatite character.
• 3. Feldspar sands. Pegmatites are complex deposits, and feldspar is extracted from them both specially and incidentally.

The largest deposits of granite pegmatites are deposits in the Russian Federation (Karelia, the Urals, the Baikal region, East Siberia, Transbaikalia, the Far East), Sweden, Norway, the USA and other countries. Nepheline pegmatites are known in the Urals (Vishnevogorsk deposit, etc.). There are large deposits of granite pegmatites in Ukraine (Eliseivsk, Zelenaya Mohyla).

4. Mining

Feldspar output in 2005. Click the image for the details.

At the end of the twentieth century. in the world there was an increase in production of s.l. (Demand for feldspar in ceramics to increase / / Skill. Mining Rev. - 2000. - 89, 2. - R. 8.). World production n.l. in 1998 it amounted to 11.5 million tons, of which 63% in China, Italy, Japan, Turkey and the USA. Commercial mining of nepheline syenite is carried out mainly in Canada and Norway. In ceramic production, consumption of s.sh. and nepheline syenite is approximately 5.5 million tons / year or 41% of total demand. The expected growth in consumption is approximately 10% per year. In the glass industry, the consumption of feldspar and nepheline syenite is approximately 5,750,000 t/y, with an overall reduction in demand due to increased use of cullet.

The history of the origin of the name is specially researched by Zenzen and Spencer. The term was first introduced by Tilas in 1740 - feldtspat, from Swedish feldt or fait (field, arable land) and German spath (plate, bar). In the "Mineralogy" of Vallerius, another term is proposed - feltspat, from Swedish, felt (moraine field, glacial valley) and spat (tablet, cleavage punch). In the German translation of Wallerius' Mineralogy (1750), the term is modified as feldspath ("feldspar"), and in English (1772) as fieldspar. As a result of their mixing, the modern term appeared - feldspar. In addition, the 2nd edition of Kirwan's Mineralogy (1794) uses the term felspa, from the German fels (rock, rock), i.e. "rock-forming" spar.

Less commonly used terms are: felspar (English), feldspath (French).

Chemical composition

According to the chemical composition, feldspars are aluminosilicates and consist of aluminum oxide (Al 2 O 3), potassium oxide (K 2 O), sodium oxide (Na 2 O) or from Al 2 O 3, Na 2 O and calcium oxide (CaO ) in combination with silicon dioxide (SiO 2 ).

Feldspars are the main rock-forming minerals of many igneous, metamorphic and sedimentary rocks with the chemical composition M[T 4 O 8], where M is alkaline, M + = (H, Li, Na, K, Rb, Cs, Tl, 4) + or alkaline earth, M 2+ \u003d (Ca, Sr, Ba, Pb, En) 2+ cations, and T - Si 4+ or replacing it in an endless silicon-oxygen skeleton (A1, B, Fe, Ga) 3+, (Ge) 4+ , performing the anionic function in [TO] 4 -tetrahedra, compensating the charge of M-cations.

Varieties

Feldspars are classified according to their chemical composition, crystal structure and structural state (Si/Al-ordering), which exhausts all their “structural-chemical varieties”. It is advisable to single out “mineral species”, their “varieties” (by chemical composition, structural modifications, morphological features, physical properties) and types of “block-crystals”.

Feldspars are 50-60 May. % of the earth's crust; they, along with quartz, olivine, micas, pyroxenes, and amphiboles, are among the most common rock-forming minerals. Their significance is extraordinary. Among them, potassium-sodium (alkaline) feldspars are distinguished, constituting a subgroup of orthoclase, which includes orthoclase proper, sodium orthoclase, microcline, anorthoclase, sanidine, adularia, and calcareous-sodium, or sodium-calcium, feldspars (plagioclase subgroup).

Form of being in nature

All feldspars are characterized by growth twins (intergrowths, intergrowths), as well as transformation twins resulting from phase transformations in feldspar block crystals.

In normal twins (face law), the twin axis is perpendicular to the fusion plane, which is both the twin plane and the plane of symmetry of the twin (usually the most common face). In parallel twins (the law of the axis), the twin axis lies in the twin fusion plane, which can be any face lying in the zone, the edge of which is the given twin axis. In complex twins (complex laws), the twin axis is perpendicular to one of the edges and lies in some important crystallographic plane, which is the twin fusion plane.
Sometimes Carlsbad-A (fusion plane - (010)) and Carlsbad-B (fusion plane - (100)) twins are distinguished. The Aclinic-A law is considered as a special case of the Pericline law with the fusion plane (001), and the Ala-A and Ala-B laws are considered as a special case of the Esterel law with the fusion planes (001) and (010).
The most common are twins with the (010) intergrowth plane. For monoclinic Potassium feldspars, Carlsbad, Manebach and Baven twins are most characteristic, for triclinic (Potassium feldspars, Na-feldspars, plagioclases) - albite, as well as periclinic and Carlsbad. Albite and periclinic twins in monoclinic feldspars are impossible due to their symmetry (a good diagnostic feature). On the contrary, they are common in triclinic feldspars.
The position of the "rhombic section" depends on the chemical composition of the feldspar. For this reason, the orientation of the albite-pericline twins in the microcline and in the essentially sodic alkali feldspar - anorthoclase is different: under a microscope in the microcline in sections along (010) only periclinic twins are observed (at an angle of 83 section along (100) - only albite twins (parallel to cleavage cracks along (010)), and in section along (001) - a lattice of albite and pericline twins at an angle of 90° (microcline lattice)", in anorthoclase in sections along (010 ) only periclinic twins are also observed, but they are almost parallel (at an angle of only 2-5°) to cleavage cracks along (001), in the section along (100) - a lattice of albite and periclinic twins at an angle of 90°, and in the section along ( 001) - only albite twins parallel to cleavage cracks along (010).
Complex twins are widespread in feldspars, for the study of which Vardanyants developed a special theory of “twin triads”.
A structural explanation for twinning was given by Taylor et al. using orthoclase as an example. The twins are connected through oxygen atoms common to both twinned individuals, and due to the fact that they are located on common symmetry elements, the growth of a single single crystal continues, as it were (in the orientation of each of the twinned individuals). In this case, there is no rupture or significant distortion of the quadruple rings of [(Si,Al)O 4 ]-tetrahedra in the framework of the structure. In Manebach twins, the (010) symmetry planes coincide in both individuals, and the common oxygen atoms O(Al) lie on common axes of rotation. In Baven twins, the common oxygen atoms O(А2) are located on the (010) symmetry planes or deviate from them by only 0.2 A, while the symmetry planes themselves in twin individuals are oriented at an angle of 90°. In Carlsbad twins, two common oxygen atoms O(Al) and O(A2) lie respectively on the axis of rotation and the plane of symmetry (010) of one of the individuals, and the other pair of common atoms O(Al) and O(A2) lie on the axis and plane (010) of the second individual. Since the O(Al) atom at a height of 4.7 A in the twin and in the single crystal is in the same position (the Si-O-Si-O chains in the twin differ from the configuration in the single crystal only by a slight rotation of the oxygen atoms around the silicon atoms in - and -tetrahedra at heights of 4.1 and 5.05 Å), intergrowth twins (“contact twins”) are formed along the (010) plane. However, since it is also a plane of symmetry, “right” and “left” twins are possible. And since the same position is occupied by O(Al) atoms at a height of 1.8 A in the Si-O-Si-O chain of the second twin individual, in this case twins of “growth” are also possible.

Albite and pericline twins in triclinic feldspars, according to Taylor et al., are obtained respectively by reflection in the (010) plane or by rotation about an axis that is close to perpendicular to (010). Therefore (especially in the case of polysynthetic twinning or simultaneous albite-pericline twinning), the twin increases its symmetry to monoclinic. For albite-pericline twins in the microcline (“M” twins, “microcline” lattice), this is evidence of its formation from primary monoclinic feldspar as a result of solid phase transformations. In monoclinic feldspars, albite and periclinic twins are impossible, since = perpendicular to (010).

Aggregates.

Physical properties

Optical

Color. The color of feldspars is varied, as a rule, light: white, yellowish, greenish, reddish, brownish. Green and bluish-green varieties are called amazonite. Amber-yellow ferruginous feldspars are described.

Transparency. Transparent, water-transparent.

Refractive indices

Ng = , Nm = and Np =

Mechanical

Hardness. 6-6.5.

Density. 2.54-2.57 for potassium feldspars, 2.62-2.65 for albite, 2.74-2.76 for anorthite, up to 3.4 for celsian. Intermediate values ​​are for K,Na- and Ca,Na-feldspars.

Cleavage. All feldspars have cleavage in two directions - at an angle of 90 ° or slightly different from a straight line (20 "- in microcline, 3.5-4 ° - in plagioclases), as a rule, perfect along (001) and perfect or good along ( 010) In these directions, the smallest number of tetrahedral bonds per unit area breaks, only bonds between chains of tetrahedra are broken, but quadruple rings are preserved.

Chemical properties

Feldspars are acid-resistant, do not dissolve in acids other than HF (K-feldspars and albite), or easily (anorthite) or hardly (basic plagioclases) decompose in concentrated HCl with the release of a gelatinous precipitate of silica.

Other properties

Some feldspars have the ability of opalescence (adularescence), aventurism or labradorescence, which in the domestic literature is generally called iridescence. Opalescence gives shimmer in bluish, greenish, pearl white and pale yellow tones in K,Na-feldspars. (cryptoperthites) (moonstones) and oligoclases (belomorites) or iridescent play of light in bluish-lilac or gray-blue tones, reminiscent of the ebb of feathers on the neck of a dove (oligoclases-peristerites), and is caused by the perthite structure of alkali feldspars or a similar phenomenon of phase decomposition in oligoclases. Labradorescence is a similar phenomenon in Labradors (one of the synonyms for Labrador is tavusit, from the Persian “tavusi” - peacock). Aventurism - a bright glow of the mineral with point highlights in orange-red, bright yellow and raspberry tones (sun stones), caused by the reflection of light from small scattered plates of hematite (in K-feldspars, albite or oligoclase), ilmenite or native copper (in labradors ).

Artificial obtaining of a mineral

The synthesis of alkali feldspars of composition (Na, K, Rb, NH 4 )[(Al, Ga, Fe, B)(Si, Ge) 3 O 8 ] is usually carried out from glasses of stoichiometric composition dry (at a temperature of 700-1000 °) or hydrothermal (for example, 550°, 1 kbar, 140 h) way. For the first time, artificial analogs of feldspars of the compositions NaGaSi 3 O 8 , NaAlGe 3 O 8 , NaGaGe 3 O 8 (triclinic) and KGaSi 3 O 8 , KAlGe 3 O 8 , KGaGe 3 O 8 (monoclinic) were obtained in , monoclinic RbAlSi3Og - in . Feldspar of composition NaFeGe 3 O 8 could not be synthesized (pyroxene of NaFe composition crystallized instead of it under hydrothermal conditions, and pollucite instead of CsAlSi 3 O 8 . big size Cs atom, as well as Li-feldspars, but, on the contrary, due to the too small size of the Li atom (Smith and Brown, 1988). However, monoclinic CsAlSi 3 O 8 still managed to be obtained by ion exchange between analbite or sanidine and a CsCl salt melt. Lithium, hydrogen and silver feldspars were synthesized in a similar way: LiAlSi 3 O 8 , HAlSi 3 O 8 and AgAlSi 3 O 8 .

Feldspars of composition K have also been synthesized.

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Diagnostic features

Orthoclases are associated with quartz, felsic plagioclase, muscovite, biotite, and hornblende. Anorthoclases - Ti-augite, apatite, ilmenite. Plagioclases - spessartine, rhodonite, Mn - epidote, sanbornite, gillespit.

Origin and location

Feldspars are the main rock-forming minerals of igneous, metamorphic, a number of sedimentary rocks, pegmatites, metasomatites and hydrothermal veins.

Feldspars, being one of the main rock-forming minerals, crystallize as follows:
1. From igneous melts of granite, syenite, diorite, and gabbroid composition.

2. In the course of post-magmatic processes (mainly acid plagioclases and alkali feldspars) - from pegmatite melts, hydrothermal solutions, during greisenization processes.

3. By ion exchange in crystalline schists (chlorite and micaceous schists, micaceous gneissic schists and gneisses various types) as products of blastesis (Greek "blastos" - sprout, embryo, kidney) at average temperatures of the order of several hundred degrees (from a solid substrate), i.e., during recrystallization of a substance in a solid state.

The diversity of the chemical composition of feldspars served as the basis for the classification of igneous rocks. In the total composition of the earth's crust, plagioclases occupy about 40%. Acid plagioclases are constituents of continental masses of granitic composition (sial); the main plagioclases are part of the basalt-gabbroid lower layer of the earth's crust (oima).

Sanidines are characteristic of acidic and alkaline volcanic rocks: rhyolites, trachytes, phonolites, and shallow intrusions. It is believed that they are homogeneous, but modern research methods show that they are mostly sanidine-cryptoperthites. In ultrasilicic rocks, such as obsidian and rhyolite, they can form spherulites intergrown with cristobalite and bundles of acicular crystals. The metamorphic rocks are formed under conditions of sanidine facies metamorphism at high temperature and low pressure. Sometimes they are established as authigenic formations in sedimentary rocks.

Orthoclases are characteristic of acidic and alkaline plutonic and volcanic rocks, as well as pegmatites in these rocks. They are typical for metamorphic rocks of a high degree of metamorphism, contact-metasomatic formations. In the case of a high content of the sodium component, they are usually crypto- or microperthites. Formed in hydrothermal alpine veins (adularia). They are characteristic of sedimentary rocks in continental drift zones (arkose sandstones) and authigenic new formations in sediments of various compositions (including carbonate).
Microcline is a common mineral in plutonic felsic (without phenocrysts) rocks: granites, granodiorites, syenites and simple and complex pegmatites in these rocks in association with quartz, acid plagioclase, muscovite, biotite and hornblende. Characteristic of metamorphic rocks of amphibolite facies and greenschist facies. Like orthoclase, it is a common clastic mineral in detrital sedimentary rocks, but it can also occur as an authigenic formation.
High-sodium K,Na-feldspars (anorthoclases) are typical of volcanic and hypabyssal rocks formed under conditions of rising temperatures. It often forms in the peripheral rims of porphyritic oligoclase phenocrysts in alkaline syenites (larvikites, etc.) or is isolated as homogeneous K,Ca,Na-feldspars. (triple). It is usually cryptoperthitis. Associates with Ti-augite, apatite, ilmenite.
Plagioclases are widespread in almost all types of igneous and metamorphic rocks and some sedimentary deposits. Albite and oligoclase are characteristic of acid rocks: granites, granodiorites, rhyolites, syenites, granitic and syenite pegmatites. Andesine is typical for rocks of medium silicic acidity. Labradorite and bytonite are common in the main rocks: - gabbroids and basalts - and are the main mineral of anorthosites. Anorthite is less common and appears in anomalous mafic and ultramafic rocks. Metamorphic rocks usually contain acidic and intermediate plagioclases with an An content of less than 50%, but the Ca content increases in rocks with a higher degree of metamorphism. Anorthite is present in skarns and other contact metamorphosed carbonate rocks. In sedimentary rocks, plagioclases are usually present in the form of detrital grains, but albite often appears in them as an authigenic neoformation during the diagenesis of sediments.
Celsian is characteristic of metamorphic rocks of the amphibolite facies of metamorphism, rich in Mn and Ba, where it usually gradually passes into hyalophane. Spessartine, rhodonite, Mn-epidote, sanbornite, gillespit, etc. are typical in paragenesis with them. Badingtonite is a rare mineral formed from MH 4 -containing groundwater. Established in mercury cinnabar ores, rocks of the phosphorus formation, in oil shale. Forms pseudomorphs after acid plagioclase. Ridmerjnerite is a rare mineral formed when rocks are enriched with boron. It has been established as an authigenic mineral in black oil shales and brown dolomites, as well as in alkaline rocks of the Green River sedimentary formation in the USA and Darai-Piez alkaline pegmatites in Tajikistan.

Practical use

Feldspars are of great practical importance. Feldspar raw materials are used in various industries as fluxing, aluminous, alkaline or alumina-alkaline components, as well as inert fillers. Feldspar rocks are preferred with a content of K 2 O + Na 2 O more than 7 wt.%, CaO + MgO no more than 2, Al 2 O 3 more than 11 and SiO 2 63-80%. Therefore, mainly acidic (rarely medium, alkaline) aluminosilicate igneous, metamorphic or sedimentary rocks of feldspar, quartz-feldspar, kaolinite-feldspar-quartz or nepheline-feldspar composition are used as raw materials. Basic and ultrabasic rocks are practically not used.
Global reserves and resources of feldspar raw materials have not been estimated. In Russia, they currently amount to 115 million tons (52% of the reserves of the CIS countries); of which 88 million tons (76%) are granitic pegmatites. World production of feldspar raw materials is 5 million tons / year: Italy - 1500, USA - 700, France - 400, Germany - 330, Thailand - 330, South Korea- 240, Mexico - 200 thousand tons. In the world production of the CIS countries - 10-15%, of which the share of Russia is about 48%, Kazakhstan - 30, Ukraine - 15, Uzbekistan - 7%. The main volume of production in Russia falls on Karelia and the Murmansk region.
According to the content of quartz, the raw material is subdivided into feldspar proper (less than 10% quartz) and feldspar quartz (more than 10% quartz); by the ratio of alkalis - to high-potassium (“potassium module” = K 2 O / Na 2 O > 3 wt.%), used in the electrical and abrasive industries, as well as for the production of welding electrodes, potassium (“module” of at least 2), used in the electrical and porcelain industry, potassium-sodium (“modulus” not less than 0.9), used for the production of building ceramics, and sodium (“modulus” less than 0.9 or not standardized), used in the glass industry and for the production of enamels vitreous porcelain type. If nepheline is present, nepheline-feldspar raw materials are isolated.
High-potassium feldspar materials (with a high “potassium module” - above 4, low content of CaO and MgO - no more than 1.5% and FeO and Fe 2 O 3 - no more than 0.15-0.30%) are used in electroceramic production for production of high-voltage porcelain insulators, as a flux and adhesive mass for the production of grinding and grinding abrasive products, for ceramic coating (slag-forming products that stabilize the arc) in the production of welding electrodes, in porcelain and faience production to obtain transparent glaze coatings (“modulus” of at least 3). Feldspar and quartz-feldspar materials with a high “potassium module” (2-3 and above 3 for products of the highest grades) are used in the ceramic industry as a flux (flux) for the production of fine ceramics (household and art porcelain, electrical porcelain), potassium- sodium quartz-feldspar materials (with a low “modulus” up to 0.9) - for the production of building ceramics (sanitary ceramic products, facing and finishing tiles), and sodium feldspars (with a non-standardized “modulus”) - for the production of low-temperature porcelain. Quartz-feldspar and nepheline-feldspar materials are also used as a charge for the production of electrovacuum and high-grade technical glass, sheet technical and window glass, and products from dark green and container glass. Sodium feldspar materials are used for enamel coatings of cast iron and iron products, to increase their viscosity and chemical resistance.

Feldspars are used as a filler in the paint and varnish industry (the resulting paints are more resistant than with carbonate filler to acid rain and sunlight and are used for outdoor work), in rubber production, in the manufacture of opalescent glass, tiles, tiles, concrete, cement , in dentistry for the production of artificial teeth, etc.
New areas of application of feldspars (mainly from low-quality and substandard feldspar and nepheline-feldspar materials, which is important in solving environmental problems and integrated development of deposits) are the production of glass-ceramic materials (glass-ceramics and slag-ceramics used in construction, chemical, mining and electrical industry), heat-insulating materials (foam glass used in construction to insulate walls and floors, refrigerators, etc.), as well as binders (pozzol and other new cements) obtained from sistof (glass-like mass with an admixture of microcline, aegirine and others associated minerals) and sulfate-alkaline fertilizers obtained from phosphogypsum - industrial waste generated during acid (with H 2 SO 4 ) processing of Khibiny apatite-nepheline ores during the production of phosphate fertilizers. Nepheline-feldspar materials are used to produce engobe - a ceramic mass baked in the form of glazes to lightweight concrete products (wall panels, etc.).

V last years feldspars have attracted attention in connection with the problem of radioactive waste disposal. Instead of the common vitrification technology, fixation of 90 Sr, 134 Cs, and 137 Cs radioisotopes in polymineral matrix materials consisting of Sr-containing feldspar with a quartz shell or pollucite with a shell of K,Na-feldspar has been proposed; these materials are more resistant to leaching than glass.

Minerals of the feldspar group attract attention with the beauty of the color range and the unusual effects in the form of iridescence, shellirization, asterism and cat's eye.

Photo: 1 - earrings with labradorite, 2 - earrings with amazonite and enamel, 3 - diamond earrings with moonstone and adularia, 4 - diamond ring with labradorite, 5 - ring with sunstone and opals, 6 - pendant with moonstone and belomorite , 7 - pendant with carved amazonite and enamel

Moonstones and amazonite have long been successful in making jewelry in Ancient Egypt and countries of the East. As for the "sun stone" - heliolite, it became popular only at the beginning of the 21st century: its success is ahead.

Description

Feldspars are an extensive group of minerals belonging to the class of silicates. In accordance with the chemical composition, three types of feldspars are distinguished:

1. sodium-calcium;
2. potassium;
3. potassium-barium.

These minerals are widely distributed in nature and are used as raw materials for the production of rubidium and other substances, and are also used in the manufacture of ceramic and glass products. However, among feldspars there are many transparent and translucent minerals used in jewelry as ornamental stones. These include:

• belomorite - a kind of moonstone with iridescent bluish reflections - oligoclase, in which albite predominates;
• andesine - a translucent or transparent variety of plagioclase, which has a color range in shades of yellowish, pink, orange-red, light green and white;
• labrador (“peacock stone”, “tausin stone”) is a plagioclase moonstone that has a dark blue or blue-black color with iridescence in color scheme peacock feather;
• spectrolite - a kind of labrador with iridescence in the colors of the spectrum;
• "bull's eye" - a purple-brown variety of Labrador, iridescent in red;
• adularia - moonstone, which is a transparent or translucent variety of potassium spar with iridescence of a silvery-bluish hue;
• amazonite - microcline shades of blue and bright bluish-green tone;
• heliolite (“sun stone”) is a transparent or translucent orthoclase in golden yellow, orange and red hues, which has a schillerization effect, which consists in the presence of a golden sheen due to the inclusion of hematite flakes and finely dispersed copper powder in its crystals.

Feldspar stones have a hardness in the range of 6-6.5 units on the Mohs scale.

Grade

The cost of feldspars depends on the rarity of their variety, the degree of transparency, color, the presence of the effect of iridescence and shillerization on the surface of the stones and the place of their origin. For example, one gram of green-colored amazonite with a lot of inclusions costs $ 1-3, while samples of this stone of pure dark turquoise tone are valued at $ 10 or more per gram.

More expensive than other feldspars is a sun stone - heliolite, one bead of which costs $ 1.5, and a necklace made of it is estimated at $ 100.

Place of Birth

There are vast deposits of feldspar on all continents of the Earth. Tanzania, USA, Madagascar, Norway, Russia are famous for heliolite deposits. In the Russian Federation, it is mined in the Urals and Karelia.

Adularia deposits are located in such countries of the East as Sri Lanka, India, Tajikistan, as well as in Switzerland, the USA, etc.

Amazonite mining is carried out in the countries of the Central Asian region, in Ukraine, in Brazil, India, Canada, Mongolia, etc.

Labrador is mined in the territory of such countries as Ukraine, Canada, Brazil, Egypt, India, Canada, Mongolia, Norway.

Photo - rings: 1 - with amazonite, 2 - with andesite, 3 - with a sunstone, 4 - with a labrador, 5 - with a bull's eye, 6 - a ring with a labrador and black spinel

magical properties

Stones with iridescent effects have always attracted attention with their unusualness, therefore they were endowed with various witchcraft qualities. Varieties of moonstone were attributed the properties to develop in a person the ability to clairvoyance and mysticism. Amazonite was considered capable of strengthening family ties.

Medicinal properties

Feldspars are used by lithotherapists in the treatment of many diseases. Massage with amazonite balls relieves nervous tension and strengthens the cardiovascular system. Labrador is used to treat infertility, diseases of the musculoskeletal system, inflammation of the prostate. Adularia is used in the treatment of epilepsy and mental disorders.

Cut

The main type of feldspar cut for jewelry purposes is the cabochon, which reveals the beauty of the iridescence, shillerization, asterism and cat's eye effects inherent in these minerals. Transparent samples of stones can be subjected to any facet cut.

Feldspar Jewelry

The hardness of feldspars allows them to be used for the manufacture of all types of jewelry and jewelry - rings, necklaces, earrings, bracelets, brooches, beads. For setting stones that have a color or iridescence in cold colors of blue, bluish, silvery shades, a frame made of white gold, silver, cupronickel, medical alloy, etc. is used. Stones painted in warm colors are set in red or yellow gold.

Imitations and fakes of feldspars

Heliolite is imitated using glass, which contains copper flakes. To imitate adularia and belomorite, frosted glass is used, which scatters light, but does not have the characteristic bright sparkles that are characteristic of natural stones.

Who are feldspars for?

Jewelry with light moonstones - belomorites and adularia - will look great on platinum blondes, especially the Summer color type. However, they are also suitable for brunettes. Bright amazonites, which are colored in green tones, and orange-red heliolites will be in harmony with the appearance of brown-haired women, brunettes and women with hair color with shades of "burgundy", "mahogany" (Autumn color type). For owners blonde hair with a yellowish tinge and red-haired women, amazonites of light green tones and stones of yellow-orange hues (autumn and spring color type) are suitable.

Astrologers recommend wearing jewelry with adularia to representatives of the signs of Water - Cancers and Pisces, with amazonite - to Gemini, Aquarius, Libra. As for the rest of the feldspars, there are no instructions, so everyone can afford to wear them.

Diverse in color and effects, feldspars attract the attention of jewelry lovers with their unusual appearance, which makes it possible to give the image originality and originality.

Feldspar is a common mineral compound in the lithosphere. Features of formation, chemical and mineral composition determine its use in various branches of industrial production, jewelry.

Feldspar is a common mineral compound in the lithosphere

The mineral compound that takes part in the formation of rocks is the most common in the upper part of the lithosphere. Its share in the composition of igneous rocks is 50-60% of the volume.

The mineral feldspar in clastic rocks gives way only to a silicate compound (quartz). Hydration of minerals is accompanied by the formation of sericite, kaolinite, zeolites, etc.

There are known cases of formation of other products of feldspar alteration depending on pressure, temperature and composition of brines affecting the rock. Diagnostics of minerals is carried out by an optical method at the microscopic level.

The hardness of mineral formations is 6-6.5, the density is 2.5-2.8. The color range of spars ranges from white to bluish and red. The translucent mineral has a vitreous luster, perfect cleavage.

The mineral feldspar in clastic rocks gives way only to the silicate compound

Feldspar, the origin of which is associated with the transformation of solid solutions, has a number of varieties. Most minerals make up an isomorphic series of alkaline chemical elements (potassium, sodium), in which the following formations are distinguished:

• orthoclase;
• albite;
• anorthite.

Feldspar, whose properties depend on the fractional content of orthoclase and anorthite, has 2 isomorphic modifications:

• alkali spars (contain potassium and sodium);
• plagioclase (calcium and sodium are present).

Molecules of anorthite and albite can form homogeneous mixed crystals in any proportion, regardless of the state of aggregation (liquid or solid). The result is a continuous series of calc-sodium feldspars (plagioclases).

Features of feldspar (video)

Orthoclase and albite are mutually miscible in all proportions at high temperatures and limited at a low temperature gradient. Orthoclase and anorthite, in contrast, almost do not mix in the crystalline state, even at high temperature gradients.

Crystals containing varying amounts of orthoclase and barium feldspar (celsian) also occur naturally, but complete miscibility of the group has not been proven and cannot be taken into account.

The continuity of the albite-anorthite series manifests itself at a high temperature gradient. At low temperatures perthite, microcline and orthoclase are formed. High-temperature formation is sanidine, which is characterized by a tabular habit, perfect cleavage.

When the mineral is destroyed, an uneven conchoidal fracture is formed. The formula of sanidine is K(AlSi3)O8. Iron, sodium, calcium and water are included as impurities in the composition of the formation. The mineral often forms Carlsbad twins.

The continuity of the albite-anorthite series manifests itself at a high temperature gradient

Compared to quartz, feldspars are not stable, but are constant compared to nepheline and olivine.

Classification of mineral formations

The diverse chemical composition of feldspar served as the basis for the classification of known rocks. It is this mineral that is the main rock-forming component of pegmatites, gneisses, many metasomatic formations, and crystalline schists.

Chemically, the mineral belongs to aluminosilicates containing Na, K, and less often Ca. Microclines and orthoclases represent a group of potassium formations. In a small amount, the mineral contains impurities of iron, lithium, cesium, strontium, magnesium.

Sodium and calcium spars belong to plagioclases and appearance resemble microclines. The complex formula of plagioclases reflects their chemical composition (Ca, Na)(Al, Si)AlSi2O8.

Gallery: feldspar stone (30 photos)

Minerals are part of igneous and metamorphic rocks dominated by microcline formed at low temperatures. The sequence of their participation in the formation of formations depends on the conditions and geological conditions.

For example, albite, often found in veins of pegmatite formations, is formed by the presence of plagioclases. Under the influence of hydrothermal solutions in the process of destruction and weathering of rocks, they are converted into kaolins and sericite (mica).

Potassium feldspar (KAlSi3O8) depending on the placement of chemical elements in the crystal lattice, forms the following rows:

• orthoclase;
• adularia;
• microcline;
• sanidine.

Among the varieties of low-temperature orthoclase is known semiprecious stone adularia (moonstone) which is characterized by opalescence and amazonite (light green microcline).

Potassium feldspars and plagioclases differ from each other. To establish such a difference, it is necessary to use the staining method. To do this, hydrofluoric acid is applied to the prepared rock surface or a plate made from it.

After processing, the rock sample is placed in a special solution that stains the plagioclase red.

For example, pegmatites contain microcline and orthoclase along with quartz and muscovite. The presence of beryl in the mineral enriches the compound with beryllium, which replaces silicon along with aluminum.

The description of written granite fully corresponds to the name. Intergrowths of orthoclase with quartz in appearance resemble written characters.

Potassium spars are resistant to the environment, but they can be replaced by other mineral formations as a result of metasomatism.

A rare type of mineral formation is potassium-barium feldspar. A rare mineral forms individual crystals of light Brown with collection value.

Potassium spars are resistant to environmental influences

Practical use of rock

A mineral compound is mined from deposits of granite and granite gneisses. Feldspar deposits are known in Norway, Sweden, Madagascar, the USA (Maine), Russia (Southern Urals).

Mineral microcline is mined in the Russian Federation, Poland, in Germany, Japan. Jewelry amazonite is mined in Canada, India, Brazil, Africa. Labrador deposits are concentrated in the vicinity of Tibet (China), Canada, India, and Finland.

The best raw material for use in production is a feldspar mineral with a content of potassium and sodium oxides of at least 8% with a K2O:Na2O ratio of 1.5:2 with an admixture of iron oxide of not more than 0.2% and calcium oxide of not more than 2%.

The use of feldspars in the manufacture of porcelain improves the quality of products and gives them better performance properties. The mineral is used as a raw material in the glass industry for the manufacture of special and optical grade glass.

The mineral is used for the production of ceramics, the manufacture of certain types of rubber, high-voltage insulators, glasses, welding electrodes, abrasives, and as a filler in the production of toothpastes.

The most expensive stones in the world (video)

It is known the use of feldspars as a raw material for the extraction of rubidium and other chemical elements contained in them.

Some types of mineral formations with iridescence and an optical effect of opalescence are an ornamental material for making jewelry.

Due to the wide color spectrum, processing and polishing features, the material is used for the manufacture of interior decor elements, mosaics and paintings.

Attention, only TODAY!

Feldspar is a mineral known to the layman more by ear than by sight, and even more so by touch. Yes, mineralogists, noting the endless variety of silicates attributed to spars, have thoroughly studied no more than a dozen species - and prefer to operate with other, narrow terms.

But feldspars account for half of the mass of the earth's crust and two thirds of its volume! Many of the rocks are in fact varieties of spars mixed with various mineral additives.

Word from Sweden

The expression "feldspar" is a tracing-paper from the German feldspat, where feld is "field" and spat is a layered, fractured, lamellar stone. Curiously, the German mineralogical term was formed from the Swedish name, because it is in Sweden - and not at all in Germany - that agricultural land located on old moraines is literally dotted with pieces of lamellar stone.

The word "cleavage" in Russian mineralogy comes from Swedish-German roots, and in general should be pronounced as "spar". To an unprepared listener, "cleavage" sounds almost like "solidity", although the meanings of "cleavage" and "solidity" are diametrically opposed.

Some of the feldspars are beautiful

Minerologists combine a great variety of minerals into a group of spars, distinguishing them according to their elemental composition. Gemologists follow an empirical path, highlighting stones from feldspars worthy of becoming an ornament.

Any of the feldspars is theoretically colorless and unattractive - as it should be for silicon compounds. However, without impurities, such minerals are practically not found, and therefore many of the spars are very attractive in appearance.

Feldspar classification

According to their chemical composition, feldspars are subdivided into potassium, potassium-barium and sodium-calcium, also called plagioclases. There are many different plagioclases; gemologists emphasize albite, which is integral part sun stone. Albite crystals are valued for their rarity.

Even more rare is the Celsian mineral - potassium-barium spar, which occurs as inclusions in metamorphic massifs. Green or greenish-brown Celsian has no jewelry value, since it is opaque, but as a collection material it is highly valued.

Origin of feldspars...

...exclusively magmatic. The predominance of feldspar in the planet's crust is evidence of its turbulent volcanic past, complicated by large-scale cosmic catastrophes. Who knows with what mineral composition the native planet would surprise people, if it were not for the events that led to the formation of the moon.

By the way, there is as much feldspar on the Moon as on Earth. Many meteorites also contain feldspar.

Due to the extreme prevalence of the mineral, its mining is carried out on all continents. The best Labradors come to the market from Canada and Greenland - although Ukraine, Brazil and India provide many good quality stones. Fine amazonite, dyed in alternating turquoise and beige colors, was found in South America, but is mined in the Russian north and in igneous outcrops of the Baikal region.