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 Microcline (and sometimes Orthoclase).

Types of Perthites

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.

 

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

 

Type

• Perthite - Intergrowth of Albite (or Oligoclase) and Microcline
• Amazonite-perthite - Intergrowth of Albite (or Oligoclase) and green Microcline
• Orthoclase-perthite - Intergrowth of Albite (or Oligoclase) and Orthoclase