An X-Ray Investigation of the Felspars

Taylor, W. H.; Darbyshire, J. A.; Strunz, H.

doi:10.1524/zkri.1934.87.1.464

Cited by 22 publications

(13 citation statements)

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“…Taylor's model of the archetypal structure of feldspars, induced from X-ray diffraction (XRD) data of sanidine (Taylor 1933;Taylor et al 1934), suggests a monoclinic C2/m average symmetry if the framework of tetrahedra is idealized in a topology where the actual occupancy of T sites by Si and Al atoms is disregarded. The structure consists of three-dimensionally linked SiO 4 and AlO 4 tetrahedral units with two crystallographically nonequivalent tetrahedral sites, T 1 and T 2 .…”

Section: Introductionmentioning

confidence: 99%

Medium-range order in disordered K-feldspars by multinuclear NMR

Sánchez-Muñoz

Sanz

Sobrados

et al. 2013

American Mineralogist

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The structures of K-rich feldspar, (K>Na)AlSi 3 O 8 , are currently described as "ideal" crystals with periodic average structures from Bragg diffraction maxima obtained by reciprocal-space techniques. Polymorphism is explained by variable substitutional disorder of framework Si and Al cations in tetrahedral T sites, and positional disorder of cavity alkali cations in a single M site. Here, highresolution magic angle spinning multinuclear magnetic resonance spectroscopy, leading to 29 Si, 27 Al, and 23 Na spectra at 9.4 as well as 27 Al, 39 K, and 23 Na spectra at 19.6 T, has been used to investigate the "real" structures along the order-disorder series of K-feldspar crystals. The "ideal" and "real" structure coincides only in the perfectly long-range ordered triclinic end-member of the low-microcline structure. Long-range disordered structures (either with monoclinic or triclinic symmetry by X-ray diffraction) show non-random disorder at the medium-range scale, triclinic-like distortions with four sets of T sites for framework atoms, two sets of M sites for alkali atoms, and Al-O-(K,Na) multi-site correlations by NMR spectroscopy. The K-feldspar structures can be described by a medium-range structure using the number of Al atoms per four-membered rings of tetrahedra, with "…-2-0-2-0-…" chains for microcline and orthoclase where the Al-occupancies t 1 O > t 2 m > t 2 O ≈ t 1 m, and with "…-1-1-1-1-…" chains for valencianite and sanidine, in which t 1 O > t 2 m ≈ t 2 O ≈ t 1 m. Framework cations respect Loewenstein's rule (Al-O-Al avoidance), as well as some additional constraints of charge dispersion involving deficiency of Si atoms in Q 4 (4Si,0Al), (1Si,3Al), and (0Si,4Al) environments, constraints which are particularly strong in valencianite. These "real" structure features cannot be described by "ideal" structures owing to the lack of resolving power of the reciprocal-space techniques.

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Section: Introductionmentioning

confidence: 99%

Medium-range order in disordered K-feldspars by multinuclear NMR

Sánchez-Muñoz

Sanz

Sobrados

et al. 2013

American Mineralogist

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“…I t has been suggested by Taylor et al (1934) th a t the plagioclases do not form a simple isomorphous series between albite and anorthite as end-members, and further work now in progress in this laboratory confirms this view; a comprehensive classification cannot yet be attem pted.…”

Section: Resultsmentioning

confidence: 84%

The lamellar structure of potash-soda felspars

1940

Proc. R. Soc. Lond. A

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The structures of some typical members of the felspar group were determined by Taylor, Darbyshire and Strunz (1934), and an attempt was made to explain the characteristic twinnings and the nature of the lamellar inter-growths known as perthites and microperthites. These authors emphasized that the Carlsbad, Manebach, and Baveno types of twin, which appear in monoclinic as well as in triclinic felspars, should be regarded as quite distinct from the albite and pericline types which are of frequent occurrence in the triclinic felspars. For in these last types the twinned triclinic individuals are merely simulating the higher symmetry of the monoclinic structures: thus for example in an albite twin the individuals are related by reflexion in the plane (010) which is actually a symmetry plane of the monoclinic crystal, while in a pericline twin the individuals are related by rotation about the b -axis [010] which is a digonal axis in the monoclinic structure. The formation of Carlsbad, Manebach, or Baveno twins is a consequence of certain special features of the structure, and is not due to the simulation of higher symmetry.

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“…They seem to have in fact a tetrahedral framework characterized by an ordered alternation of Si and Al tetrahedra [this was experimentally confirmed in the case of anorthite (TAYLOR, DARBYSHIRE and STRUNZ, 1934;MEGAW, KEMP-STER and RADOSLOVICH, 1962) and for celsian (GAY, 1956; NEWNHAM and MEGAW, I960)] which causes the doubling of the c parameter and the appearance of weak "superlattice" reflections in their x-ray diagrams.…”

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confidence: 89%

Single-crystal x-ray investigations on strontium feldspar

Bruno¹

1970

Zeitschrift Für Kristallographie - Crystalline Materials

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AuszugMit Hilfe von Einkristall-Methoden wurden an synthetischen Kristallen von Strontium-Feldspat Überstrukturreflexe vom Typ b beobachtet und damit die vermutete Gitterkonstante von 14 Ä bestätigt. Als Raumgruppe wurde 12/c bestimmt, wodurch die Annahme gestützt wird, daß der Strontium-Feldspat isostrukturell mit Celsian ist. Ein Karlsbader Zwilling wurde röntgenographisch nachgewiesen. AbstractThe crystal structure peculiarities of strontium feldspar were confirmed experimentally by a single-crystal x-ray analysis on synthetic crystals. Type b superlattice reflections were found and the length of the c parameter (14 Ä) was confirmed. The space group is I 2/c and this affirms the supposition that strontium feldspar is isostructural with celsian. A crystal twinned according to the Carlsbad law was found and examined. The complete diadochic substitution Ca-Sr and Sr-Ba, found in the aluminosilicates with formula (X,Y) [AI2S12O8] and described in several recentarticles (BRUNO and GAZZONI, 1968; BRUNO and GAZ- ZONI, 1969; NAGER, HOFFMANN and NISSEN, 1969; NAGER, BAMBATJERand HOFFMANN, 1970), made us wonder whether also the monoclinic phase SrAl2Si20s would be approximately isostructural with the calcium and barium feldspars. For the monoclinic compounds BaAl2Si20e and SrAl 2 Si 2 08, in particular, the closeness between unit-cell parameters and the strict resemblance of frequencies and intensities in the relative infrared spectra make it very likely that they are isostructural. It had still to be experimentally proved, however, that also strontium feldspar has c ~ 14 Ä. Such a value is demanded by Brought to you by | New York University Bobst Library Technical Service Authenticated Download Date | 7/15/15 10:04 PM

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An X-Ray Investigation of the Felspars

Cited by 22 publications

References 1 publication

Medium-range order in disordered K-feldspars by multinuclear NMR

Medium-range order in disordered K-feldspars by multinuclear NMR

The lamellar structure of potash-soda felspars

Single-crystal x-ray investigations on strontium feldspar

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