In polarized-light microscopy with crossed polars and an anisotropic mineral in the light train, when the two electric vectors (permitted light or vibration directions) of a 1135 randomly oriented crystal are each parallel to those of the polars, no light is transmitted and the crystal is at extinction. Isotropic crystals and anisotropic crystals viewed parallel to an optic axis remain extinct upon stage rotation, while randomly oriented anisotropic crystals go extinct four times upon stage rotation of 360 degrees . Compare: anisotropy; extinction angle; extinction direction; inclined extinction; optic axis; parallel extinction; undulatory extinction.