oligoclase

[ ol-i-goh-kleys ]

Phonetic (Standard)IPA

noun

, Mineralogy.

a kind of plagioclase feldspar occurring commonly in white crystals, sometimes shaded with gray, green, or red.

oligoclase

/ ˈɒlɪɡəʊˌkleɪs /

a white, bluish, or reddish-yellow feldspar mineral of the plagioclase series, consisting of aluminium silicates of sodium and calcium. Formula: NaAlSi 3 O 8 .CaAl 2 Si 2 O 8

oligoclase

/ ŏl′ĭ-gō-klās′,ō′lĭ- /

A white to gray triclinic mineral of the plagioclase feldspar group. Oligoclase occurs in igneous rocks with a relatively high silica content, such as granite. Chemical formula: (Na,Ca)(Al,Si)AlSi 2 O 8 .

First recorded in 1825–35; oligo- + -clase

C19: from oligo- + -clase

These intermediate members are the lime-soda felspars known as oligoclase, andesine, labradorite and bytownite.

The felspar of the granulites is mostly orthoclase or cryptoperthite; microcline, oligoclase and albite are also common.

The felspar ranges from bytownite to oligoclase, being usually a variety of labradorite; orthoclase is scarce.

At Danbury the mineral occurs with microcline and oligoclase embedded in dolomite.

Amelia Court House, Virginia, is another locality whence come pieces either of orthoclase or oligoclase exhibiting this property.

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