Rectangular glass substrate and method for preparing the same

A rectangular glass substrate having a front surface, a back surface, four side surfaces, and eight chamfered surfaces defined between the front surface and each of the side surfaces and between the back surface and each of the side surfaces, wherein

• the substrate includes a first curved surface along an edge line between the front surface and at least one of the chamfered surfaces disposed adjacent thereto, having an average gradient of up to 25% in a range from the front surface to a position of 50 μm below the front surface when the substrate is rested horizontal with the front surface facing upward, and a second curved surface along an edge line between at least one of the four side surfaces and one of the chamfered surfaces each disposed adjacent to the front surface, having an average gradient of at least 30% in a range from the at least one side surface to a position of 50 μm below the at least one side surface when the substrate is rested horizontal with the at least one side surface facing upward,
• the substrate has a thickness of at least 6 mm, and
• each of the side surfaces includes a plane which is perpendicular to a plane including the front surface and a plane including the back surface in the rectangular glass.