good question... but not so easy. I don´t have very much information on him. Perhaps others have.
Grindstone was a Hunkpapa chief at Standing Rock in the 1880ies. According to the Mary Collins Family Papers at the South Dakota State Archives he was a village herald and "friend of the missionaries". Grindstone and his band were present at the Battle at the Little Bighorn in 1876 and surrendered shortly after with others like Elk Head (Red Hair), the Pipe Keeper. It is said he was a friend of the Mission at Little Eagle (Running Antelope’s Village), Grand River, SD.