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Anortoclasa: Este mineral, perteneciente a la serie de los feldespatos alcalinos, se da en forma de cristales prismáticos o tabbulares cortos, comúnmente con maclas. Se encuentran ejemplares masivos, lamelares, granulares o criptocristalinos. Se forma principalmente en rocas volcánicas ígneas. (Na,K)AlSi3O8
Lower temperature terminations of the three-phase region plagioclase-alkali feldspar-liquid January 1, 1962 Geological and experimental evidence indicate that the three-phase field, plagioclase-alkalifeldspar-liquid, may terminate in several different ways. The possible terminations have been developed from Schreinemakers' rules governing the ...
The microperthites formed a ~< 590~ by heterogeneous nucleation of thin albite films which coarsened to> 1~tm length. Cryptoperthites developed at < 400~ by homogeneous ucleation of sub-~tm long ...
Alkali feldspars are framework silicates characterized by a network of (Si,Al)O 4 tetrahedrons linked to one another in all directions. The structure of alkali feldspar can …
The alkali feldspars include monoclinic feldspars (orthoclase and sanidine) and triclinic feldspars (microcline and anorthoclase). At high temperatures, it is possible to form …
The heat transport properties of feldspar, one of the major minerals of the crust, are important for constraining the thermal state of the Earth's crust. The thermal diffusivity (D) and thermal conductivity (κ) of two natural alkali feldspars, namely, perthite and albite (Ab), were simultaneously measured at high temperatures (300–873 K) and …
feldspar, any of a group of aluminosilicate minerals that contain calcium, sodium, or potassium. Feldspars make up more than half of Earth's crust, and professional literature about them constitutes a large percentage of the literature of mineralogy. Of the more than 3,000 known mineral species, less than 0.1 percent make up the bulk of Earth ...
The effect of microstructures on laboratory K-feldspar dissolution at alkaline hydrothermal conditions has been reported by, e.g., Locati et al., 2010, and more recently in a detailed study by Ciceri et al., 2017b. Dislocations and exsolution lamellae create localized regions of higher strain, which cause these crystallographically …
As noted, both alkali feldspar and plagioclase exist in a wide range of igneous rocks. But, feldspars with compositions in the middle of the feldspar ternary (shown in white in Figure 6.53) are rarely found because they unmix to form coexisting alkali feldspar and plagioclase. There is a large miscibility gap in the ternary system.
Abstract and Figures. A series of single-phase alkali feldspars in the system Na2O-K2O-Al2O3-SiO2-H2O were crystallized from dehydrated gels at 500 bars and …
The equilibrium partitioning of Na and K between alkali feldspar and NaCl–KCl salt melt was determined at 800 $$^circ$$ ∘ C, 850 $$^circ$$ ∘ C, 900 $$^circ$$ ∘ C, 950 $$^circ$$ ∘ C and 1000 $$^circ$$ ∘ C and close to ambient pressure. Four different natural gem-quality alkali feldspars with low degree of Al–Si ordering …
data for alkali feldspar and SiO 2 phases from 2 clasts found in Apollo sample 15405,78. For alkali feldspar, data from 4 regions of interest (ROI) are presented, taken from 2 different clasts.
The boundary between the core albite and the K-feldspar replacement is sharp and decorated with numerous pores. The distribution of Na and K, determined by electron probe microanalysis, is uniform within the core and rim and has an abrupt discontinuity at the interface. No evidence exists for K-Na interdiffusion at the resolution …
Alkali Feldspar Granite. Granite is a medium-tocoarse-grained acid igneous rock with essential quartz (>20%) and feldspar, where alkali feldspar constitutes between 100 and 35% of the feldspars, and minor mafic minerals. Hornblende and biotite are the commonest mafic minerals, however, muscovite is also frequently encountered.
Modified date: 23/04/2023. Feldspar is the name of a large organization of rock-forming silicate minerals that make up over 50% of Earth's crust. They are discovered in igneous, metamorphic, and sedimentary rocks in all components of the sector. Feldspar minerals have very comparable structures, chemical compositions, and bodily properties.
Alkali feldspars constitute a solid-solution between K-feldspar o orthoclase molecule (Or) and albite (Ab), which represents also the sodic end-member of the plagioclase series. Anorthite (Ca[Al 2 Si 2 O 8]; An) is present in small quantities in alkali feldspars, usually constituting less than 5% of the solid solution and predominantly found in Na-rich alkali …
In alkaline medium, all the feldspar samples show a similar trend presenting both exothermic peaks. The first peak with lower heat flux is observed between the 2–3 h after mixing aluminosilicate and activation solution. As in the acidic medium, the first peak corresponds to the initial rapid dissolution of different particles. ...
3D zoning of barium in alkali feldspar. Abstract Interpretation of chemical zoning within igneous minerals is critical to many petrologic studies. Zoning in minerals, however, is commonly observed in thin sections or grain mounts, which are random 2D slices of a 3D system. Use of these 2D sections to infer 3D geometries requires a set of ...
At high temperatures the alkali feldspars form a solid-solution with continuous miscibility between albite and sanidine. At temperatures below about 600°C and low pressure a miscibility gap exists (see Fig. 1), and alkali feldspar of intermediate composition tends to exsolve into an association of a sodium-rich and a potassium-rich …
The degree to which the observed alkali-feldspar dissolution rate enhancement in the presence of organic acids can be accounted for by the aluminum-depleted precursor mechanism described above can be assessed by an evaluation of the experimental data reported by Welch and Ullman (1993) and Stillings et al. (1996).These …
be computed from the observed c value of an alkali feldspar (c.J and its composition as cr: cot" + 0.038(l - N*). For natural feldspars, c* varies from about 7.180 A for high sanidine to approximarely 7.222 A for maximum microcline. The distribution of Al and Si between the T, and T, tetrahedral sites of an alkali feldspar
Feldspar structures are based on SiO 4 and AlO 4 tetrahedra linked to form a three-dimensional framework. They form two series that share one end-member …
Partition coefficients (Min/L D) for a series of geochemically relevant elements have been calculated from combined EMP/LA-ICP-S analyses of plagioclase, alkali feldspar, Ti-magnetite, biotite, apatite, and trachytic/trachyphonolitic melt pairs in selected Campi Flegrei rocks.Pl/L D and Kfs/L D values are generally very low for most of the …
The alkali feldspars are major components of granites and granite pegmatites. The study of their structural state and composition has always been one of interesting researches in petrology and mineralogy [1–3].Pioneering works by Barth (1969) [] and Laves (1952) [], where alkali feldspar composition and structure were correlated with the …
A pegmatite ore (with the Li 2 O grade being 1.56 %) was obtained from the mines of western Sichuan, China. The XRD and multi-elemental chemical analysis results of the ore were presented in Fig. 2 and Table 2.It can be seen in Fig. 2 and Table 2 that the valuable mineral was spodumene, and the primary gauge minerals were feldspar, quartz and …
At high temperatures alkali feldspars form a complete series of solid solutions with monoclinic symmetry between albite and K-feldspar. On cooling, different intracrystalline processes may occur and we consider that the evolution of perthitic textures is determined by minimizing strain energy. It is possible to calculate the strain energies involved in …
Alkali Feldspar. The alkali feldspars are those within the alkali feldspar solid solution series. In thin section, alkali feldspar grains often appear to be sprinkled with dirt (PPL) or tiny confetti (XPL). Feldspars weather …
The feldspar structure contains an average of one aluminum (A1) for every three silicon (Si) ions; but, in different feldspars (q.v.), the Al shows varying degrees of preference for a particular tetrahedral site. Where the Al ions are randomly distributed throughout the tetrahedral sites, the structure is disordered; if the Al ions are situated in a preferred …
Alkalifeldspar is a group of minerals that are composed of alkali metals, silicon, oxygen and sometimes other elements. They are important rock-forming minerals in igneous and metamorphic rocks. Find out more about their properties, varieties, occurrences and associations at mindat, the largest and most comprehensive mineral database online.
Feldspar - Mineral Composition, Uses, Types: All the rock-forming feldspars are aluminosilicate minerals with the general formula AT4O8 in which A = potassium, sodium, or calcium (Ca); and T = silicon (Si) and aluminum (Al), with a Si:Al ratio ranging from 3:1 to 1:1. Microcline and orthoclase are potassium feldspars (KAlSi3O8), usually designated …
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