Results 141 to 150 of about 542 (177)
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South-western Granites and Alkali-Feldspar Megacrysts
Nature, 1969BOOTH has extended his conclusions concerning the Land's End granites to the other granitic masses of south-west England and has raised several points that require further consideration1. These include his sweeping correlation between the granite bosses, the nucleation and growth of metasomatic alkali feldspars and the distribution of potassium between
M. STONE, C. S. EXLEY
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Dislocation formation and albitization in alkali feldspars from the Shap Granite
American Mineralogist, 1997Orthoclase-rich alkali feldspars in the Lower Devonian Shap granite, northwest England, contain two generations of albite-rich feldspar. These have partially replaced earlier exsolution microtextures consisting of albite lamellae (coarse semicoherent albite films and fine coherent albite platelets) in tweed orthoclase.
Martin R. Lee, Ian Parsons
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Alkali feldspars from part of the Galway granite, Ireland
Mineralogical Magazine, 1972SummaryThe structural states of alkali feldspars from the eastern end of the Galway Granite show transitions from orthoclase to microcline as a result of late deformation. Analyses of twenty samples for SiO2, Al2O3, TiO2, Fe2O3, CaO, Na2O, K2O, S, Cu, Zn, Ga, Rb, Sr, Ba, and Pb agree with previously determined orders of entry of elements into the ...
J. R. Wilson, J. S. Coats
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Ordering and unmixing of alkali feldspars in a porphyritic granite and its country rocks
TMPM Tschermaks Mineralogische und Petrographische Mitteilungen, 198250 alkali feldspars from a Variscan porphyritic granite and 27 from two country rocks of Caledonian and Variscan age respectively have been investigated for their bulk chemistries and their structural states. Ordering is illustrated in thebc-plot afterStewart andWright (1974); unmixing is illustrated in a newly designed diagram with the Or-contents of ...
G. Propach, L. R. Adloff
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The Identification of Granitic Fire-Cracked Rocks Using Luminescence of Alkali Feldspars
American Antiquity, 1999The question of Fire-Cracked Rock (FCR) in Woodland contexts has become an important and controversial topic in Western Great Lakes archaeology. There are no clear and widely accepted criteria for distinguishing FCR when the rocks show no observable characteristics associated with fire (heating and cooling).
George (Rip) Rapp +2 more
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Gahnite and columbite in an alkali-feldspar granite from New Zealand
Mineralogical Magazine, 1981AbstractGahnite and columbite with compositions (Zn5.96Fe1.55Mg0.21Mn0.13)Σ7.85Al16.09O32and (Nb7.36Ta0.60Mn2.95Fe0.98Ti0.09)Σ11.98O24occur as accessory phases in a highly evolved garnetiferous muscovite alkalifeldspar granite. Both phases have developed as a result of a concentration of Zn, Nb, and Ta during the fmal stages of the fractional ...
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Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite
Mineralogical Magazine, 1995AbstractAlkali feldspar phenocrysts (bulk composition Or75.0Ab24.6An0.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto- and micro-perthites with altered, micropore-rich feldspar with irregular microstructures.
Martin R. Lee +2 more
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Petrogenetic Significance of Alkali Feldspar Megacrysts and their Inclusions in Cornubian Granites
Nature, 1968Petrogenetic Significance of Alkali Feldspar Megacrysts and their Inclusions in Cornubian ...
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Lattice structural variation in K-feldspar megacrysts of associated charnockite and alkali granite
Mineralogical Magazine, 1982AbstractThe perthite megacrysts from charnockitic and non-charnockitic members of a sialic intrusive complex in the Varberg area of south-west Sweden have been investigated by powder X-ray diffraction. The extent of Al/Si order in the K-feldspar host lattices of the megacrysts is restricted in all but the major alkali granite differentiate.
D. R. Iball, F. H. Hubbard
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Journal of the Geological Society, 1997
Alkali feldspar phenocrysts in the Lower Devonian Shap granite are compositionally and microtexturally zoned. Most of each phenocryst has exsolved to form microperthite with an approximate bulk composition of Or 72 Ab 28 An <1 , but sub-millimetre wide zones within ...
M. R. LEE, I. PARSONS
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Alkali feldspar phenocrysts in the Lower Devonian Shap granite are compositionally and microtexturally zoned. Most of each phenocryst has exsolved to form microperthite with an approximate bulk composition of Or 72 Ab 28 An <1 , but sub-millimetre wide zones within ...
M. R. LEE, I. PARSONS
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