Microcline is the low-temperature polymorph of the potassic feldspar group, and commonly occurs in granitoid rocks.  A cluster of sub-equant microcline grains dominates the central portions of these figures.  Microcline is colourless and has low relief in plane light (A) similar to plagioclase and quartz also present in these images.  Both the microcline and plagioclase here are somewhat cloudy due to development of secondary mica as an alteration product (termed sericite), which is coarser in the plagioclase here.  Well-developed “cross-hatch” twinning according to pericline and albite twin laws, diagnostic of microcline, is evident in B, in which the grains show their maximum interference colours of first order white.  Note the “spindle shape” of these lamellae (i.e., they thicken and thin along their length) that is unlike similar crossed twins present in some plagioclase grains in other rocks, in which the lamellae are more consistent in their thickness along their length or simply taper (see Plagioclase).  Sample is from a two-mica granite from an unknown location.  Both views are 2.2 mm across.  A ppl, B x-nicols.