Leucite occurs as phenocrysts (commonly euhedral) in alkaline mafic volcanic rocks and less commonly in hyabyssal intrusions.  The coarse, euhedral colourless leucite phenocryst in these figures shows negligible relief relative to plagioclase occurring as inclusions and in the basalt groundmass.  The extremely low birefringence of leucite is apparent in B, in which the characteristic complex lamellar twins are also present.  This sample is a leucitite from Aroiccia, Italy.  Both views are 5.5 mm across.  A ppl, B x-nicols.