This is a cleavage rhomb of a much larger [orthoclase](http://webmineral.com/data/Orthoclase.shtml) crystal [(K,Na)AlSi₃O₈]. Since it is only part of crystal, it does not show the characteristic simple twinning of orthoclase. However it does display two near perfect cleavages and a third weaker one. It also displays the characteristic perthitic texture of exsolved orthoclase, with narrow exsolution 'stringers' of plagioclase throughout.