"Tatanka" Native American Stone Sculpture

I just got this piece at estate auction where I purchased seven or eight pieces of art by many listed artist. This is a stone sculpture of a Buffalo. I could use some help in identifying the stone, I am guessing rose color alabaster, with pipestone horns? It measures about 8' long and about 6' tall.
It has a medicine wheel carved on one side. I found the design and proportions very pleasing. The bottom is signed with very light scratching, and hard to read, making me think that it is a harder stone and not something like soapstone. The bottom reads Tatanka, which is Sioux for Buffalo, Little White Man, Oglala Sioux. I haven't been able to find anything on this artist.