microcline–microperthite

Microcline is a common feldspar mineral, a form of potassium aluminosilicate (KAlSi₃O₈) found in igneous rock. Green varieties are known as amazonstone and are sometimes used as gems. Microcline is distinguished from other feldspars by its unique tartan twinning. It is the form of potassium feldspar most stable at lower temperatures.1

Microcline can form mixtures with albite, a sodium-rich feldspar. When these mixtures are intergrown, they are called microcline–microperthites. In microperthite, the sodium and potassium phases separate into minute intergrowths that are only visible under a microscope. Perthite, a related term, describes similar intergrowths where the separation may be visible to the naked eye.123