Anorthoclase

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Anorthoclase
2V angle
Measured: 34°–60°
References[2][3][4]

The mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline

alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi3O8 and between 64 and 90 percent of NaAlSi3O8.[5]

An anorthoclase crystal from Mount Erebus, Antarctica

Structure and stability

Anorthoclase is an intermediate member of the high

exsolution occurs and a perthite structure results.[6]

Occurrence

Anorthoclase occurs in high temperature sodium rich

hypabyssal (shallow intrusive) rocks. The mineral is typically found as a constituent of the fine grained matrix or as small phenocrysts which may occur as loose crystals in a weathered rock.[2]

It was first described in 1885 for an occurrence on

Trapani Province, Sicily. The name is from the Greek αν-, ορθός and κλάσις (not cleaving at right-angles), for its oblique cleavage.[2][3]

See also

References

  1. S2CID 235729616
    .
  2. ^ a b c "Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2016-03-04. Retrieved 2011-12-04.
  3. ^ a b "Mindat.org".
  4. ^ "Webmineral data".
  5. ^ Deere; Howie; Zussman. Framework Silicates. Rock Forming Minerals. Vol. 4. Wiley. pp. 2–5, Fig. 1.
  6. ^
    ISBN 0-471-80580-7
    .
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