Microcline

Microcline may be chemically the same as monoclinic orthoclase, but because it belongs to the triclinic crystal system, the prism angle is slightly less than right angles; hence the name "microcline" from the Greek "small slope." It is a fully ordered triclinic modification of potassium feldspar and is dimorphous with orthoclase. Microcline is identical to orthoclase in many physical properties, and can be distinguished by x-ray or optical examination. When viewed under a polarizing microscope, microcline exhibits a minute multiple twinning which forms a grating-like structure that is unmistakable. Perthite is either microcline or orthoclase with thin lamellae of exsolved albite. Amazon stone, or amazonite, is a green variety of microcline. It is not found anywhere in the Amazon Basin, however. The Spanish explorers who named it apparently confused it with another green mineral from that region. The largest documented single crystals of microcline were found in Devils Hole Beryl Mine, Colorado, US and measured ~50x36x14 m. This could be one of the largest crystals of any material found so far. Microcline is commonly used for the manufacturing of porcelain.