GRINDSTONE

To provide a grindstone that has high durability, is less likely to form a deep cutting flaw in a workpiece and can restrain heat generated during processing.SOLUTION: A grindstone contains composite abrasive grains. The composite abrasive grains include first composite grind abrasive grains with first abrasive grains in a first binding material, and a plurality of the composite abrasive grains are bound to each other by another binding material so as to have pores opening on a surface. The composite abrasive grains may further include second composite abrasive grains with second abrasive grains fixed on surfaces of rubber particles by a second binding material. In that case, a mass ratio (B/(A+B)) of the content (B) of the second composite abrasive grains to the total quantity (A+B) of the content (A) of the first composite abrasive grains and the content (B) of the second composite abrasive grains may be 0.8 or less.SELECTED DRAWING: Figure 1 【課題】耐久性が高く、被加工物に深い切削痕が形成されづらく、加工時に発生する熱を抑制可能な砥石を提供すること。【解決手段】複合砥粒を含有する砥石であって、前記複合砥粒は、第１の結合材に第１の砥粒が分散した第１の複合砥粒を含み、表面に開口する気孔を有するように、複数の前記複合砥粒が他の結合材により互いに結合している、砥石。前記複合砥粒は、さらに、第２の結合材によりゴム粒子の表面に第２の砥粒が固定された第２の複合砥粒を含んでいてもよく、その場合、前記第１の複合砥粒の含有量（Ａ）および前記第２の複合砥粒の含有量（Ｂ）の合計量（Ａ＋Ｂ）に対する、前記第２の複合砥粒の含有量（Ｂ）の質量比（Ｂ／（Ａ＋Ｂ））が、０．８以下であってもよい。【選択図】図１