Abstract: Inclusions occurring in leucites from the Oscar and Zirkel Mesa leucite lamproites consist of high (>10 wt.%) and low (<4 wt.%) K₂O discrete glass phases which are interpreted to have resulted from silicate liquid immiscibility. Both glasses are quartz-normative and rich in Ti, Fe, Mg, Ca and Ba and poor in A1. The high-K glass is strongly peralkaline. Neither of the glasses have compositions representative of any known lamproites. These inclusions represent the first described examples of silicate-silicate immiscibility shown by glass in alkaline rocks.