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perthite

Perthite is an intergrowth of two different Feldspar minerals in one rock. Perthite is usually composed of veins or stripes of one feldspar running through a different feldspar. There are many different types of Perthite. Perthite combinations are of Albite (and sometimes Oligoclase) intermixed with either Microcline or Orthoclase.



Types of Perthites:


Classified by Host:

  • Antiperthite - Perthite in which the potassium feldspar (i.e. Microcline and Orthoclase) forms first, and afterwards the sodium feldspar (i.e. Albite and Oligoclase) forms internally in the mineral.
  • Mesoperthite - Perthite in which the sodium feldspar (i.e. Albite and Oligoclase) forms first, and afterwards the potassium feldspar (i.e. Microcline and Orthoclase) forms internally in the mineral.

Classified by Size:
  • Cryptoperthite - Perthite in which the feldspar intergrowth is so fine it can only be detected with a microscope.
  • Microperthite - Perthite in which the feldspar intergrowth is very fine but it can be detected with an unaided eye.
  • Macroperthite - Perthite in which the feldspar intergrowth is large and is easily seen.

Classified by Type:


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