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feldspar
plagioclase feldspar
plagioclase feldspar One of the most important rock-forming silicate
minerals with the general formula (Na,Ca)(Al)
1–2(Si)
2–3 O
8. There is a
solid solution series (see
PLAGIOCLASE SERIES) between the two
end-members albite (Ab) (NaAlSi
3O
8) and anorthite (An) (CaAl
2Si
2O
8), and the percentage of calcium end-member present is used to subdivide the series into a number of individual minerals: albite (0–10 mol% An); oligoclase (10–30 mol% An); andesine (30–50 mol% An); labradorite (50–70 mol% An); bytownite (70–90 mol% An); and anorthite (90–100 mol% An). Albite; sp. gr. 2.61;
hardness 6.0–6.5; is whitish,
vitreous;
tabular or irregular; with two
cleavages {010} and {001} meeting at almost right angles on the (100) face; and occurs in
acid igneous rocks and
spilites. Oligoclase; sp. gr. 2.64;
triclinic; cleavage perfect basal {001}, good {010}; is similar to albite except in the percentage An it contains. Andesine; sp. gr. 2.66; triclinic; cleavage perfect basal {001}, good {010}; has properties similar to those of albite but tends to occur in more
intermediate igneous rocks. Labradorite; sp. gr. 2.67; crystals thin and
tabular, flattened parallel to (010); cleavage perfect basal {001}, good {010}; is greyish-white but may show iridescence due to lattice imperfections on cleavage faces and occurs in
basic igneous rocks. Bytownite; sp. gr. 2.72; triclinic; crystals often tabular prismatic but normally form irregular grains; cleavage perfect basal {001}, good {010}; also greyish-white, is a constituent of basic and
ultrabasic igneous rocks. Anorthite; sp. gr. 2.75; triclinic; crystals tabular and prismatic but normally form irregular grains; cleavage perfect basal {001}, good {010}; also greyish-white, occurs in basic and ultrabasic igneous rocks and in metamorphosed
limestones. These plagioclase feldspars cannot be distinguished from one another in hand specimens, but under the microscope their
extinction angles vary; this is a useful property in their identification, together with the nature of the multiple twinning (see
CRYSTAL TWINNING) which is a very characteristic feature and serves to distinguish them from
alkali feldspars.
Exsolution of potassium-feldspar in a plagioclase feldspar host is called ‘antiperthite’.
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Feldspar and nepheline syenite: fillers with a purpose.
Magazine article from: Paint & Coatings Industry; 10/1/2003; ; 700+ words
; ...is a calcium feldspar. Most commercial feldspars are produced...balance of the feldspar and nepheline...2) Milled feldspars and nepheline...coatings-grade feldspars and nepheline...in Table 2. Feldspar and nepheline...
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Quartz-feldspar separation for the glass and ceramics industries
Magazine article from: Minerals & Metallurgical Processing; 5/1/2007; ; 700+ words
; ...obtained Keywords: Feldspar, Magnetic separation...Introduction All feldspars contain silicon...after clay. Feldspar does not have...temperatures. Feldspars are used as fluxing...flotation of feldspars differently. Feldspar recovery was...
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Feldspar Market Review.
M2 Presswire; 1/6/2009; 572 words
; ...January 2009-Research and Markets: Feldspar Market Review(C)1994-2009 M2 COMMUNICATIONS...researchandmarkets.com/research/092ca9/feldspar_market_re) has announced the addition of the "Feldspar Market Review" report to their offering...
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Feldspar and nepheline syenite
Magazine article from: Mining Engineering; 6/1/2000; ; 700+ words
; US feldspar output sold or used in 1999 was an estimated 900 kt (990,000...990,000-st) level. Output included flotation concentrates, feldspar content in feldspar-silica mixtures, potash feldspar and aplite. North Carolina...
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FELDSPAR AND NEPHELINE SYENITE
Magazine article from: Mining Engineering; 6/1/2008; ; 700+ words
; U.S. feldspar output sold or used in 2007 was an estimated 700 kt...and 2003. Output included flotation concentrates, feldspar content in feldsparsilica mixtures, potash feldspar and aplite. Residential and commercial construction...
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Feldspar Market Review Includes Future Outlook of the World Feldspar Market.
Newspaper article from: Mining & Minerals; 1/23/2009; 630 words
; ...researchandmarkets.com/research/6b6451/feldspar_market_re) has announced the addition of the Feldspar Market Review report to their offering...report focuses on the study of the global feldspar markets. It provides region analysis...
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Materials handbook.(Feldspar--Microsilica)
Magazine article from: Ceramic Industry; 1/1/2004; 700+ words
; ...minerals in the feldspar group is found pure. Potash feldspars always contain...spar) and soda feldspars always contain...lime spar). Feldspar is found in...pure potash feldspar and 10% to...melting points. Feldspars of different...
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Italian feldspar testwork.
M2 Presswire; 12/19/2002; 700+ words
; ...December 2002-Gippsland: Italian feldspar testwork(C)1994-2002 M2 COMMUNICATIONS...testwork undertaken in Italy in regard to feldspar obtained from the Company's 40 Mt Egyptian Abu Dabbab tantalite-feldspar project. The Abu Dabbab Bankable...
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Understanding K-feldspar ^sup 40^Ar/^sup 39^Ar data: reconciling models, methods and microtextures
Magazine article from: Journal of the Geological Society; 9/1/2007; ; 700+ words
; ...formation of K-feldspar in conjunction with...suggest that K-feldspars will contain a variety...cannot work on any feldspar, given that it...certain proportion of feldspars (Parsons et al...appearance of the feldspar and the shape of...spectrum. klokken feldspars. The Klokken ...
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Systematic destruction of K-feldspar in deeply buried rift and passive margin sandstones
Magazine article from: Journal of the Geological Society; 7/1/2001; ; 700+ words
; ...Systematic patterns of detrital K-feldspar decline with increasing burial depth...the North Sea and USA Gulf Coast. K-feldspar destruction is predominantly by dissolution...porosity ratios. The quantity of K-feldspar destroyed during temperature increase...
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Feldspar
Book article from: World of Earth Science
...x2013; calcium feldspars form a continuum...the plagioclase feldspar series, which...orthoclase or alkali feldspar series. Feldspars containing significant...and plagioclase feldspars cleave along two...right angles. Feldspar nomenclature is...
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alkali feldspar
Book article from: A Dictionary of Earth Sciences
...2 O 8 (calcium feldspar, anorthite, or...apices. The alkali feldspars are represented...host and sodium feldspar occurs within the...In the alkali feldspars, perthitic textures...the plagioclase feldspars . The semi-precious...perthitic alkali feldspar.
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feldspar
Book article from: The Columbia Encyclopedia, Sixth Edition
...Chemically the feldspars are silicates of...these elements. Feldspar is found in association...igneous rocks. Feldspars weather to yield...found in soils. Feldspar crystals are either...The plagioclase feldspars are most commonly...Another form of feldspar, labradorite...
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feldspars
Book article from: A Dictionary of Earth Sciences
feldspars The most important group of rock-forming silicate minerals , including the alkali feldspars KAlSi 3 O 8 to NaAlSi 3 O 8 (K-feldspar to albite ) and the plagioclase feldspars NaAlSi 3 O 8 to CaAl 2 Si 2 O 8 ( albite to...
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plagioclase feldspar
Book article from: A Dictionary of Earth Sciences
plagioclase feldspar One of the most important rock...limestones . These plagioclase feldspars cannot be distinguished from...distinguish them from alkali feldspars . Exsolution of potassium-feldspar in a plagioclase feldspar host...
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