A turbine assembly comprising: a rotor comprising a plurality of turbine blades arranged in a circular array; and a stator, adjacent to the rotor, comprising a plurality of turbine vanes arranged in a circular array; wherein each turbine blade and each turbine vane comprises: an airfoil portion including a leading edge , a trailing edge , a pressure side , and a suction side ; and a platform on which the airfoil portion is disposed, the platform including a platform axis , a pressure side mateface located adjacent to the pressure side of the airfoil portion and a suction side mateface located adjacent to the suction side airfoil portion; wherein at least a portion of the pressure side mateface comprises a first geometry; wherein at least a portion of the suction side mateface comprises a second geometry; wherein the first geometry includes a first curved portion and a first straight portion adjacent to the first curved portion, the first straight portion being substantially perpendicular to the platform axis ; and wherein the second geometry includes a second curved portion and a second straight portion adjacent to the second curved portion , the second straight portion being substantially perpendicular to the platform axis ; and wherein together, the first geometry of the pressure side mateface and the second geometry of the suction side mateface reduce the likelihood of hot gaspath air entering very deeply into a space between the pressure side mateface and the suction side mateface. a rotor comprising a plurality of turbine blades arranged in a circular array; and a stator, adjacent to the rotor, comprising a plurality of turbine vanes arranged in a circular array; wherein each turbine blade and each turbine vane comprises: an airfoil portion including a leading edge , a trailing edge , a pressure side , and a suction side ; and a platform on which the airfoil portion is disposed, the platform including a platform axis , a pressure side mateface located adjacent to the pressure side of the airfoil portion and a suction side mateface located adjacent to the suction side airfoil portion; wherein at least a portion of the pressure side mateface comprises a first geometry; wherein at least a portion of the suction side mateface comprises a second geometry; wherein the first geometry includes a first curved portion and a first straight portion adjacent to the first curved portion, the first straight portion being substantially perpendicular to the platform axis ; and wherein the second geometry includes a second curved portion and a second straight portion adjacent to the second curved portion , the second straight portion being substantially perpendicular to the platform axis ; and wherein together, the first geometry of the pressure side mateface and the second geometry of the suction side mateface reduce the likelihood of hot gaspath air entering very deeply into a space between the pressure side mateface and the suction side mateface. an airfoil portion including a leading edge , a trailing edge , a pressure side , and a suction side ; and a platform on which the airfoil portion is disposed, the platform including a platform axis , a pressure side mateface located adjacent to the pressure side of the airfoil portion and a suction side mateface located adjacent to the suction side airfoil portion; wherein at least a portion of the pressure side mateface comprises a first geometry; wherein at least a portion of the suction side mateface comprises a second geometry; wherein the first geometry includes a first curved portion and a first straight portion adjacent to the first curved portion, the first straight portion being substantially perpendicular to the platform axis ; and wherein the second geometry includes a second curved portion and a second straight portion adjacent to the second curved portion , the second straight portion being substantially perpendicular to the platform axis ; and <EOS>