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 ?
Q: quartz; Ao: albite-calcium ordered; K: kalisilite; An: anorthoclase; B: brinrobertsite; F: fenaksite.
Hyalophane occurs as oscillatory zoned phenocrysts and rims on sanidine and anorthoclase phenocrysts in plagioclase phonolite (Birmingham, 1987).
The porphyritic trachyte contains phenocrysts of feldspar (sanidine or anorthoclase) up to 2 mm in size, rare clinopyroxene, and plagioclase (Fig.
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.
Juvenile crystals are the same as in unit 1.1 samples, with dominating sanidine crystals, anorthoclase glomerocrysts and poikilocrysts (Figure 10).
Anorthoclase, Na-sanidine, salite pyroxene and analcime, in decreasing volume proportions, are the major mineral phases.
Other primary minerals, such as Na-sanidine and anorthoclase were well-preserved.
These rocks were classified as alkaline rhyolites crystal-vitric tuffs, with aligned sanidine, anorthoclase, hastingsite and sphene crystals in a glassy matrix (Pardo, 2004).
Those rocks are modal alkaline-feldspar trachytes with anorthoclase and sanidine crystals in the matrix (Pardo, 2004).
A fault-bounded unit of metavolcanic rocks forms part of the eastern part of the complex, and consists dominantly of grey crystal to crystal-lithic rhyolitic tuff with phenocrysts of quartz, anorthoclase, and/or plagioclase.
Another uncommon item offered by the Fenn's were sharp, blocky crystals of labradorescent anorthoclase from the Pili mine, Camarco, Chihuahua.
Originally labeled as "sanidine," a chemical analysis conducted recently indicates a composition of [Ab.sub.58][Or.sub.42], which I guess makes them anorthoclase. Anyway, the crystals are blocky and rectangular to rather platy, with good luster and a rather plain gray color.