Help w/ identifying very large stone knife artifact found in Texas.

[History Detective]

Hi,
Can anyone please help identify this large, I am guessing stone knife? I found it on private property w/ the owners permission in San Marcos, Texas a while back but have always wondered if it had a classification name also approximate age.
Thanks in advance!

 

[History Detective]

Thanks tnmountains! This is an awesome site with lots of help and very educational ( and fun)!