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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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