This is straight off the Texas Parks and Wildlife Hunting Regulations page:
"When used to hunt turkey and all game animals other than squirrels, a projectile must be equipped with a broadhead hunting point that is at least 7/8-inch in width (upon impact) and has a minimum of two cutting edges. A mechanical broadhead must begin to open upon impact and, when open, must be a minimum of 7/8-inch in width."
No mention is made of material, so as long as your stone point is wider than 7/8", you should be good to go in TX!
I know quite a few guys that have taken deer, pigs, and other animals with a stone point here in TX. It is on my "to-do" list!
Bisch