Eduncle Geology (Mineralogy-1) Change of colour is a somewhat similar, phenomenon extending over broader surfaces, the succession of colours being produced as the mineral is turned. Certain varieties of the mineral plagioclase feldspar show these changes of colour very well, particularly a feldspar which is a major constituent of the igneous rock larvikite from southern Norway. Polished slabs of this rock are widely used as cladding panels by the building trade. The change in colour is caused by the interference of light reflected from thin plates of other minerals enclosed or exsolved in parallel planes within the feldspar crystals, Such a phenomenon is similar to that of schiller, an almost metallic lustre exhibited by the orthopyroxene minerals, particularly hypersthene, where reflection of colours takes place on mineral plates exsolved on parallel planes within the crystal. PLEASE EXPLAIN IN DETAIL.