A ceramic having a plurality of crystal grains that contain lithium and boron, the crystal grains are arranged in a planar direction, and the crystal grains have a mutually same crystal orientation with respect to the thickness direction, the ceramic having a portion defined by parallel sectional surfaces in a thickness direction, the portion being equally divided into a plurality of segments by parallel sectional surfaces in a planar direction, and when the amount of boron in each segment is compared, the thickness of a low boron concentration region, the low boron concentration region being a collection of segments displaying a boron amount of less than or equal to an average value for the maximum value and minimum value of the boron amount, is greater than or equal to 20% to less than or equal to 90% of the overall thickness of the portion.