anorthoclase


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anorthoclase

[ə′nȯr·thə‚klās]
(mineralogy)
A triclinic alkali feldspar having a chemical composition ranging from Or40 Ab60 to Or10 Ab90 to about 20 mole % An, where Or = KAlSi3O8, Ab = NaAlSi3O8, and An = CaAl2Si2O8. Also known as anorthose; soda microcline.
References in periodicals archive ?
The saprock and the greenish-grey saprolite from the lowermost part of the profile show relatively abundant smectite patches after clinopyroxene clusters, while residual primary minerals, such as anorthoclase, Na-sanidine, and accessories remain preserved.
a) Anorthoclase, sanidine and analcime were determined as the main components of the U-II/1 saprock horizon, beside a small amount of smectite (Fig.
c) The saprolite horizon U-II/3: green-coloured saprolite possesses smectite as the main component beside residual anorthoclase and sanidine.
Their distribution is controlled by the relative stability of Na-sanidine and anorthoclase feldspars during weathering, after pyroxene breakdown.
Table 1 Chemical microprobe analyses of green saprolite constituents Sample U-II/3 Clinopyroxene Na-sanidine * Anorthoclase * SI[O.
Hyalophane occurs as oscillatory zoned phenocrysts and rims on sanidine and anorthoclase phenocrysts in plagioclase phonolite (Birmingham, 1987).
Hand samples are white to red dense and welded pyroclastic rocks, poorly sorted, with up to 40 % of anorthoclase (Kfs) and sanidine (Sa) phenocrystals in a vitric-clastic ash matrix.
1 samples, with dominating sanidine crystals, anorthoclase glomerocrysts and poikilocrysts (Figure 10).
In thin section (Figure 14) they are classified as vitric and vitric-crystalline flow tuffs (Figure 5) with occasional plagioclase, anorthoclase and sanidine free phenocrysts in a vitroclastic matrix.
all samples have high contents of alkalis (7-10%), in which Na content is greater than K content, which is consistent with anorthoclase, Na-amphibole and Na-Pyroxene crystallization.
On the other hand, anorthoclase poikilocrysts with plagioclase nucleus (Figures 3A and 6F) suggest the following hypothesis (Pardo-Villaveces, 2004): (1) following Carmichael et al.
Those rocks are modal alkaline-feldspar trachytes with anorthoclase and sanidine crystals in the matrix (Pardo, 2004).