An interesting variation of the albite-microcline intergrowth known as perthite was noticed among some specimens obtained from a mineral dealer. The body of the specimen is pale flesh-red microcline. On the basal pinacoidal oio cleavage there are two intersecting sets of narrow, colorless albite strips, which are plates inserted parallel to the unit prism 1Iio (Fig. i). The peculiarity is that the two sets of albite plates are twinned with respect to each other on the albite law. This can be demonstrated by holding