Composite polycrystal

A composite polycrystal comprising:

• polycrystalline diamond formed of diamond grains that are directly bonded mutually, and non-diamond carbon dispersed in said polycrystalline diamond, wherein
• the composite polycrystal has a concentration of contained hydrogen of less than or equal to 1000 ppm;
• said polycrystalline diamond has a phase that is continuous three-dimensionally;
• said diamond grains forming said polycrystalline diamond have a mean grain size of greater than or equal to 10 nm and less than or equal to 500 nm;
• said non-diamond carbon has a mean grain size of greater than or equal to 10 nm and less than or equal to 500 nm;
• said non-diamond carbon has a percentage in said composite polycrystal in whole of greater than or equal to 0.1% and less than or equal to 30% as calculated from 100×Ig (002)/{Id (111)+Ig (002)} wherein Ig (002) is an area of an X-ray diffraction peak derived from (002) surface of said non-diamond carbon, and Id (111) is an area of an X-ray diffraction peak derived from (111) surface of said polycrystalline diamond in an X-ray diffraction profile of said composite polycrystal;
• said non-diamond carbon is either one of graphite and amorphous carbon;
• and
• the composite polycrystal has a Knoop hardness of greater than or equal to 50 GPa.