I would have to agree with DCMatt.If it were an indian artifact,most likely it would be inscribed in some way,have some way of lashing it to possibly a stick or bone(such as grooves),or it would show some signs of wear on a contact surface.
In short,I believe what you have here is the proverbial indian sex stone,or....
Just another f@#$ing rock!
Paleo10kbc
P.S. A rule that I use when I think I find something good is keep it anyway.I`ve got a great rock garden!