Composite polycrystal

A composite polycrystal comprising:

• polycrystalline diamond formed of diamond grains that are directly bonded mutually, and compressed graphite dispersed in said polycrystalline diamond, wherein
• 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 1000 nm;
• said compressed graphite has an interplanar spacing in a C axis smaller than that of normal graphite;
• said compressed graphite has a mean grain size of greater than or equal to 10 nm and less than or equal to 2000 nm;
• said compressed graphite has a percentage in said composite polycrystal in whole of greater than or equal to 0.5% and less than or equal to 35% 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 compressed graphite, 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;
• and
• the composite polycrystal has a Knoop hardness of greater than or equal to 50 GPa.