Feldspar albitized

An example of aluminosilicate weathering is the reaction of the feldspar albite to a montmor-illonite-type mineral... 

Few data on the chemical compositions of feldspars (albite, K-feldspar) are available. Fuji (1976) indicated that K-feldspar and albite in the propylite of west Izu Peninsula, middle Honshu are of nearly end member composition. Nagayama (1992) showed that K-feldspars in the Hishikari Au-Ag vein and in the host andesitic rock have different composition Na/K ratio of K-feldspars from the vein is lower than that from the host rocks. 

In an example of a sliding temperature path, we consider the effects of cooling from 300 °C to 25 °C a system in which a 1 molal NaCl solution is in equilibrium with the feldspars albite (NaAlSiaOs) and microcline (KAlSisOg), quartz (SiC>2), and muscovite [KAl3Si30io(OH)2]. To set up the calculation, we enter the commands... 

In a final application of kinetic reaction modeling, we consider how sodium feldspar (albite, NaAlSisOs) might dissolve into a subsurface fluid at 70 °C. We consider a Na-Ca-Cl fluid initially in equilibrium with kaolinite [Al2Si20s (OF )/ ], quartz, muscovite [KAl3Si30io(OH)2, a proxy for illite], and calcite (CaC03), and in contact with a small amount of albite. Feldspar cannot be in equilibrium with quartz and kaolinite, since the minerals will react to form a mica or a mica-like... 

Three MER diagrams (Figs. 2, 3, 4) collectively illustrate the mineralogical controls observed in each of the Meguma Supergroup formations. Because these metamorphosed rocks derive from proximal and distal flysch sediments, they likely once contained quartz, K-feldspar, albite, muscovite, illite, smectite (montmorillonite-beidellite), chlorite... 

Kaolin - Kaolinite 4, 5, 6, Dickite 16. 27 Mica - Biotite, Phologopite, Muscovite Illite - Illite 36, Illite-Bearing Shale Mixed-Layer Clays - Metabentonite 37, 42 Montmorillonite - 21. 22A, 22B, 24, 25, 26. 31 Feldspars - Albite, Anorthite, Orthoclase Chlorite - Chlorite... 

A consideration of natural occurrence and chemical composition of alkali zeolites allows a certain refinement of the zeolite facies concept previously proposed. The key factor is the grouping of the alkali zeolites into a continuous solid solution series. Other possible coexisting phases of similar composition are sodium and potassium feldspar, natrolite and analcite. The extent of solid solution decreases with temperature, possibly also with pressure. This effect allows the sequential series zeolite-K feldspar, zeolite-analcite-K feldspar, analcite-K feldspar-albite and eventually two feldspars to the exclusion of analcite, the alkali zeolite with the highest stability limits. 

The Hostrock and Backfill Material. Most crystalline igneous rocks, including granite and gneiss, are composed of a comparatively small number of rock forming silicate minerals like quartz, feldspars (albite, microcline, anorthite etc.) micas (biotite, muscovite) and sometimes pyroxenes, amphiboles, olivine and others. Besides, there is a rather limited number of common accessory minerals like magnetite, hematite, pyrite, fluorite, apatite, cal cite and others. Moreover, the weathering and alteration products (clay minerals etc.) from these major constituents of the rock would be present, especially on water exposed surfaces in cracks and fissures. 

Plagioclase feldspars Albite, oligoclase, andesine, labradorite, bytownite, anorthite... 

Some of the most common igneous minerals are quartz, potassium feldspars (orthoclase and microcline), plagioclase feldspars (albite, anorthite), micas (muscovite, biotite), olivine, and members of the amphibole and pyroxene groups. Many other minerals are found in igneous rocks, most of which occur in only very small amounts. These are called accessory minerals, the most common of these are corundum, pyrite, magnetite, zircon, rutile, apatite, and members of the garnet group. 

Following the keyword RATES, reactions rates and mathematical equations are listed from different references to describe the kinetics of K-feldspar, albite, calcite, pyrite, organic carbon, and pyrolusite reactions. Again, these entries have to be seen as examples that often have to be replaced or adjusted by site-specific data. 

Further examples can be found as already quoted in chapter 2.1.4.2 for K-feldspar, albite, calcite, pyrite, organic carbon and pyrolusite in the data set PHREEQC.dat or WATEQ4F.dat with the keyword RATES. There, all parameters are marked as comments by means of the sign in the block KINETICS. 

Lee J. I. and Lee Y. I. (1998) Feldspar albitization in Cretaceous non-marine mudrocks, Gyeongsang Basin, Korea. Sedimentology 45, 745-754. 

The pure members of the feldspar group are (refer to Table 7) sodium feldspar (albite, triclinic) — Na20. AI2O3. 6 SiO ... 

Quartz K-feldspar Na-feldspar (albite) Ca-feldspar (anorthite)... 

The composition of feldspar in a particular rock as calculated from the major element chemistry of the rock using a specific set of rules - the (CIPW) normative calculation. The feldspar content is expressed in terms of the weight % proportion of the Na-, K- and Ca-feldspars (Albite (Ab), Orthoclase (Or) and Anorthite (An)) Basalt from an arc environment which typically has about 20 wt% Al203, rather than the ca. 15 wt% found in oceanic basalts... 

The feldspars are subdivided into two groups the alkali feldspars (including mi-crocline, orthoclase, and sanidine), in which potassium is dominant with a smaller proportion of sodium and negligible calcium and the plagioclase feldspars, which vary in composition in a series that ranges from pure sodium feldspar (albite) through to pure calcium feldspar (anorthite) with negligible potassium. Feldspars form colourless, white, or pink crystals with a hardness of 6 on the Mohs scale. 

Some minerals are denominated as feldspars (albite, andesine, anorthite, and k-feldspar), halides (halite), clay minerals (kaolinite), carbonates (calcite, dolomite), and sulfates (anhydrite). 

By far the most important rock minerals are feldspars, which constitute about 60% of the igneous rock. They are essentially made of three fundamental types of minerals albite NaAlSi30g, orthoclase KAlSi30g, and anorthite CaAl SiO. Their structures are continuous three-dimensional network of [SiO ] and [AlO ] tetrahedrons, interspersed by positively charged sodium (Na(I)), potassium (K(I)), or calcium (Ca(II)). Albite and anorthite mix in arbitrary proportions such mixed minerals are known as plagioclase feldspars. Albite and orthoclase also make mixtures they are alkali feldspars. 

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