k feldspar zoning

  • Zoned Plagioclase Exercise - Teaching Examples

    The purpose of this exercise is to: become familiar with the various types of zoning found to occur in plagioclase feldspars, be able to recognize and identify the various zoning types, and be able to interpret the petrogenesis of the various zoning types from optical and microprobe data.


    OSCILLATORY EPITACTIC-GROWTH ZONING IN BIOTITE AND MUSCOVITE FROM THE LAKE LEWIS LEUCOGRANITE, SOUTH MOUNTAIN BATHOLITH, NOVA SCOTIA, CANADA ... Its main minerals are quartz + albite + K-feldspar ± topaz + four fluorine-rich mica phases: Bt 1, an early magmatic biotite as inclusions in quartz, Bt 2, the main pleochroic dark mica, ...

  • Pb isotopic zoning of K-feldspar megacrysts determined by ...

    Apr 01, 2005· 4.1. Pb isotopic zoning of K-feldspar megacrysts. Under the operating conditions used in this study signal sizes on 204 Pb were on the order of 50 mV, which largely constrains the analytical errors (and reproducibility) of ratios using 204 Pb, which are typically on the order of 0.07% (750 ppm).

  • Pb isotopic zoning of K-feldspar megacrysts determined by ...

    Pb Isotopic Zoning of K-Feldspar Megacrysts used as the external standard. Standards were repeatedly ana- lyzed every 10 –15 analyses and were analyzed twice at the Under the operating conditions used in this study signal sizes beginning of each run. Silicon, which was determined by on 204Pb were on the order of 50 mV, which largely ...

  • Feldspar - Wikipedia

    Solid solutions between albite and anorthite are called "plagioclase", or more properly "plagioclase feldspar". Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Albite is considered both a plagioclase and alkali feldspar.

  • Gallery of Feldspars -

    Green feldspar is always K-feldspar, a variety called amazonite. Field workers generally just write down "K-spar" and leave it at that until they can get to the laboratory. Igneous rocks in which the feldspar is all or mostly alkali feldspar are called syenite (if quartz is rare or absent), quartz syenite or syenogranite (if quartz is abundant

  • Mineral Zoning, P T X M Phase Relations, and Metamorphic ...

    Sample ET-10 (Figs 4–6) contains ortho- and clino- of the zoning in this sample to that in sample AS-31, pyroxene megacrysts, plagioclase, K-feldspar, meta- which contains negligible garnet, suggests that at least morphic ortho- and clinopyroxene, garnet, biotite, oxides some of the Al and Fe/(Fe+Mg) zoning in the and a trace of hornblende.

  • Feldspar - Chemical composition |

    Sanidine is a single-phase alkali feldspar; although frequently described chemically by the formula (K, Na)AlSi 3 O 8, most analyzed specimens of sanidine range between Or 50 and Or 80. (This designation is used to specify the fractions of the constituents.

  • GMS - Zoning in Minerals

    This type of zoning may also be produced by physical inclusions of rock or other minerals. An example of this would be clay, hematite, or chlorite inclusions coating the surface of an inner layer of crystal growth. Concentric zoning may be more subtle as with garnet and feldspar, for example.

  • Optical Mineralogy - Department of Geosciences

    Times New Roman Arial Wingdings Times Default Design Optical Mineralogy Feldspars Plagioclase Feldspar Alkali Feldspar Ex-Solution Perthites Perthite Photo Zoning Normal or Continuous Zoning Discontinuous Zoning Reverse Zoning Oscillatory Zoning Twinning Carlsbad Twinning Carlsbad Twin Photo Albite Twinning Albite Twin Photo Pericline Twining ...

  • Crystallization of the Shap Granite: evidence from zoned K ...

    Textural, chemical and Sr isotopic studies of feldspars from the subsolvus Shap granite, northern England, demonstrate that a number of magma mixing events have dominated the evolution of this pluton. K-feldspar megacrysts are phenocrysts formed in the magma chamber. They contain a number of Ba-rich zones that developed during periods of slight dissolution and regrowth linked to the ...

  • Feldspars Flashcards | Quizlet

    Plagioclase Zoning. Plagioclase crystals are often complexly zoned As they are part of a solid solution series, the composition across the crystal may vary in terms of the Ca and Na content ... K-feldspar - altered to clay minerals e.g. kaolinite and illite alteration appears as turbid in PPL and speckled in XPL.

  • Origin of K-feldspar megacrysts in granitic rocks ...

    of K-feldspar crystallization. In basic to intermediate rocks, where K-feldspar is a common residual phase, Ba in K-feldspar is relatively high (e.g., Trzcienski and Kulick, 1972). The same is true for pegmatites if sufficient Ba is available, even though K-feldspar is commonly a primary phase (e.g., Afonina and Shmakin, I 9 70; Schmakin, I 97 ).

  • Igneous Minerals - Union College

    Hint: to highlight K-feldspar, switch to a medium or low magnification objective (usually 4 or 10X works well), mostly close the substage iris, and raise the stage slightly (yes, raise). Though the image will be somewhat out of focus, the low index K-feldspar grains will be surrounded by bright Becke lines just inside the grain boundaries.

  • Types of Wall Rock Alteration ~ Mining Geology

    Apr 30, 2015· Ø Not all K-feldspar alteration is characterized by the presence of reddish colouration. 2. ... The product of this is a zoning of different alteration products arranged symmetrically around the central vein. In some deposits this zoning is conspicuous and may be an excellent guide to ore. ... Types of Wall Rock Alteration Types of Wall Rock ...

  • Can alkali feldspar exhibit oscillatory zoning - ResearchGate

    Dear Ahmed Morad: surely also alkali feldspar can show zoning patterns. Just look at the accepted phase diagram for the system Albite-F.K. and notice that it is composed of two merging "loops ...

  • Mechanical Instabilities and Physical Accumulation of K ...

    K-feldspar crystallography in metamorphic K-feldspar ( Figure 3a, b ); (6) euhedral plagioclase inclusions, as opposed to rounded plagioclase inclusions in metamorphic K-feldspar; (7) fractured megacrysts in which the fractures truncate zoning and the megacryst is surrounded by other crystals grown from a melt ( Figure 3a, b ); (8) evidence

  • Perthite microstructure in magmatic alkali feldspar with ...

    Feldspar megacrysts from the Weinsberg granite (Moldanubian Zone) show oscillatory zoning with respect to the albite- and orthoclase components. All growth zones show perthitic exsolutions which take the form of bleb- and lens shaped albite-rich precipitates in an orthoclase-rich host.

  • Alkali Feldspar: Mineral information, data and localities.

    Lee, M.R. and Parsons, I. (1997) Compositional and microtextural zoning in alkali feldspars from the Shap granite and its geochemical implications. Journal of the Geological Society of London: 154: 183-188. ... S., Kunz, M., Armruster, T., Schefer, J. & Hanni, H. (2005): Cation distribution in a Fe-bearing K-feldspar from Itrongay, Madagascar ...

  • Feldspar Distinctions, Characteristics & Identification

    Aug 10, 2019· Alkali feldspar (also called potassium feldspar or K-feldspar) has a color range from white to brick-red, and it's typically opaque. Many rocks have both feldspars, like granite. Cases like that are helpful for learning to tell the feldspars apart. The differences can be subtle and confusing.

  • Microchemical and Sr isotopic investigation of zoned K ...

    Microchemical and Sr isotopic investigation of zoned K-feldspar megacrysts: Insights into the petrogenesis of a granitic system and disequilibrium crystal growth. Download. Microchemical and Sr isotopic investigation of zoned K-feldspar megacrysts: Insights into the petrogenesis of a granitic system and disequilibrium crystal growth ...

  • Hydrothermal Alteration and Mineralization Zoning in Iron ...

    feldspar veins. This assemblage is late, and only cut by the latest chlorite±sulfide veinlets. The zone of Ca(-K) alteration overlaps with the zone of K-silicate alteration, but clearly postdates the earlier potassic assemblages. The dominant alteration in the envelope on the Tigresa structure is intense chlorite±magnetite±sulfide replacing

  • The mineralogical characteristics of the hydrothermal ...

    is clear. This zoning is associated with the zoning of the specific mineralizations. In the central part of the stock, the potassic alteration (K-feldspar+biotite), associated with disseminations of pyrite and chalcopyrite, is emphasized for a porphyry-copper system. …

  • Plagioclase zoning as an indicator of magma processes at ...

    Abstract. Back-scattered electron (BSE)-derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at Bezymianny Volcano, Kamchatka, based on the 2000–2007 sequence of eruptive products.


    2. REPLACEMENT OF PRIMARY PLAGIOCLASE BY SECONDARY K-FELDSPAR AND MYRMEKITE Lorence G. Collins email: [email protected] ... lacks strong zoning, shows no apparent fractures, and exhibits no K-feldspar islands. Under cathodoluminescence, however, fractures are visible, ... K-feldspar to grow inside the altered plagioclase crystal which ...

  • Deciphering textural and chemical zoning of K-feldspar ...

    This indicate that the chemical zoning in the K-feldspar megacrysts reproduces both the different degree of hybridization of the magmas, and the heterogeneity of the primary mafic magmas that periodically refilled the trachydacitic magma reservoir of Mt. Amiata volcano (Conticelli et al., 2015; Poli and Peccerillo, 2016; Van Bergen, 1985).

  • Microchemical and Sr Isotopic Investigation of Zoned K ...

    BibTeX @MISC{Growth03microchemicaland, author = {Disequilibrium Crystal Growth and D. Gagnevin and J. S. Daly and G. Poli and D. Morgan}, title = {Microchemical and Sr Isotopic Investigation of Zoned K-feldspar Megacrysts: Insights into the Petrogenesis of a Granitic System}, year = {2003}}

  • Author's personal copy -

    K-feldspar, but absent from or rare in metamorphic (solid-state) K-feldspar; (b) oscillatory zoning (Fig. 5), which is very common in igneous megacrysts, but absent from or rare in K-feldspar porphyroblasts in metamorphic rocks; (c) euhedral inclusions of plagioclase (Figs. 4 and 5), which tend to be rounded in metamorphic K-feldspar (Fig. 6),


    The Ti This study, which combines results of investigations distribution in quartz of the Land's End granite shows of the trace-element zoning of plagioclase-mantled no relationships between the Ba-zoning in K-feldspar K-feldspar and coexisting quartz phenocrysts of three or the formation of a rapakivi texture.


    Alex Strekeisen - I vetrini della mia fantasia. Zoning The zoning is a compositional variations found in the crystals. Minerals belonging to a continuous solid solution such as: plagioclase, olivine, clinopyroxene, amphibole, typically develop a compositional zoning during growth, manifested as changes in physical properties (optical) of crystals.

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