Looks like you have a Clearfork tool (clearfork culture). Such large rough chiped pieces like this were used a wedges for splitting wood/logs. A general tree harvesting tool. A small percentage of these type tools are more finely worked (the way a good Kerrville knife is worked), and the finer ones usually have one blunt end for striking with a maul (used like a big chisel for shaving and splitting). I do not know of any present value guide for them, however I am told that they will become more valuable, as do all indian made tools.
The Clearfork culture was First described in the early 1940's, followed by several other papers up to about 56. The studies estimate the earliest beginnings in the late Archaic through the woodland, and ending somewhere in the Mississippian Period. So, anywhere from about 3,500 to 1,000 years BP. The peak of the culture appears to have been during the woodland period. The site studies are on file with the Texas Archeological Society, and TARL.