ABSTRACT
The K0.97 Rb0.03Sc(MoO4)2 single crystal cross-section (0001) has been studied with an optical microscopy to determine temperature changes of domain configuration through the ferroelastic phases. The domain pattern found in the lowest ferroelastic phase is not fully consistent with the monoclinic symmetry. Four domain types observed differ in the orientation of optical indicatrix axes as well as in the value of birefringence. It has been suggested that in the third ferroelastic phase monoclinic and triclinic systems coexist in K0.97 Rb0.03Sc(MoO4)2.