microcline

[Pref. micro-, and Gr. klinō =to bend, to incline; Ger. mikroklin.] Min.: A name originally given by Breithaupt to a felspar which gave the angle of 90° 22' to 90° 23' between the two cleavage planes instead of 90°. Des Cloizeaux has referred this felspar, however, to orthoclase, but has adopted the name for a new species of felspar, having the following charac ters: Crystallization triclinic, with polysynthetic twinning. A section cut parallel with the base shows a peculiar reticulated structure, due to the regular intergrowth of twin lamelle; it incloses irregular bands of albite. Composition: Silica, 64.30; alumina, 1970; sesquioxide of iron, 074; potash, 15.60; soda, 0'48; lo on ignition, 0.35= 101-17; represented by the formula, K[Al2]Si6O16. A large part of felspar, hitherto regarded as orthoclase, is included in this species, as also much of the amazonstone and chester lite (q. v.).