A vehicular interior prismatic rearview mirror assembly includes a mirror casing and a prismatic reflective element disposed at the mirror casing and comprising a glass mirror substrate. The mirror substrate has a forward rounded perimeter region that is contactable and viewable by the driver of the vehicle and that provides a rounded transition between a front surface and a perimeter edge of the substrate. The mirror substrate has a rear perimeter edge region chamfered to form an angled surface between the rear surface and the perimeter edge. A reflector coating and a protective coating are disposed at the rear surface. An encapsulant is disposed about a perimeter region of the rear surface so as to encompass and overlay a portion of the angled surface and the reflector coating and the protective coating at the rear surface, with no part of the encapsulant being disposed at the forward rounded perimeter region.