From The University of TX Anthropology Dept.---
“Groundstone” artifacts were used for several thousand years, so in general they are fairly common; that one is kind of unusual though. My guess is they took advantage of a void left by a natural inclusion (producing the really distinct cup shape) and it was subsequently shaped by frequent use. It may have been multi-functional—it very well could have been used for dressing antler billets along with a mortar/pestle-type function (grinding ochre and whatnot for paint, grinding herbs for medicine, etc.). Mortars and pestles (some of which are impressed directly into exposed bedrock for grinding acorns and/or xerophytic plants) have been found in central Texas archeological sites, although more slab-like metates with manos tend to occur more frequently. In this area, I doubt if it would have been a fire stone.
