bytownite


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bytownite

[′bī·tau̇‚nīt]
(mineralogy)
A plagioclase feldspar with a composition ranging from Ab30 An70 to Ab10 An90, where Ab = NaAlSi3O8 and An = CaAl2Si2O8; occurs in basic and ultrabasic igneous rock.
References in periodicals archive ?
The plagioclase phenocrysts (bytownite, [An.sub.75]) are idiomorphic, slightly zoned of 3-4 mm length, comprising around 3% of the rock volume.
The specific surface area in all size fractions increased in order: quartz (no cleavage), olivine (less regular cleavage {001}), albite < oligoclase, bytownite (cleavage of feldspars {00} and {010}) < hornblende, diopside (stark crossing cleavage {110}).
The core composition for all three types of crystals, as determined mainly by extinction angle methods, is bytownite for units A, C, E and G; labradorite for unit B and oligoclase for unit D.
In the groundmass, there also occur very small plates of plagioclases: labradorite ([An.sub.68-56] [Ab.sub.41-32] [Or.sub.51]), rare bytownite ([An.sub.74-72][Ab.sub.28-26]), and andesine (samples no.