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: