It looks like a spear head someone threw away when it was only partly done, probably because it split in such a way that the finished head could not be shaped correctly. I wondered if I was just imaging this scenario. Was this a partially finished, or just a piece of flint?
Below I've pasted in part of an article from http://www.belchalwell.org.uk/artifacts-flint.asp. This is about knapped flint from the eastern hemispere, but I would think it should also apply to flints worked in Texas. My spear head (if that's what is was going to be) has ripples, bulbs of precussion, secondary working (see right edge of upper photo), fissures. Hard to see how it could be anything other than knapped flint.
I've been told that there was once a spring in our back yard. This is not difficult to believe. San Pedro Springs park with its spring-fed swimming pool is less than half a mile from here. It's easy to imagine a group of people spending time here, toward the top of the hill overlooking the San Antonio River bottom. To imagine that someone sat in the same place as I was sitting when I planted the phlox, making spear heads, talking. I wonder if he cursed when the flint cracked and ruined his spear head. Of if he just shrugged, "Meh," tossed it away and pulled another piece of flint from his bag. I say "he" and "his" because I'm pretty sure men made the spear and (later) arrow heads and did the hunting and fighting.