By means of an optical investigation of Cr-Cl boracite crystals in polarized light it has been found that an orthorhombic mm2 phase is induced by stress, generated at the mech. non-matching cubic (.hivin.43m)/tetragonal (.hivin.42m) interface, during the first order phase transition at T1 = 264 K. Elec. field studies under simultaneous optical control have shown that the orthorhombic mm2 phase can also be induced in the entire temp. range of the non-polar .hivin.42m phase above an elec. threshold field strength of about 90 kV cm-1. On the basis of optical domain observations and elec. measurements, a revised elec. field strength/temp. phase diagram is proposed and discussed.