That looks a lot like slag ("trash metal") that I've found (also in Texas, in a park that used to be a WW1 training camp before soldiers were sent off). Sometimes those slag castoffs actually contained a good amount of precious metals, you might want to test it to see!
Edit: Since you are:
1. finding this all over your property
2. It didn't cut with a torch
3. You are finding similar metal in rocks on your property
I'd ABSOLUTELY test it (even just acid tests, cheap on amazon), as well as testing the minerals you can visibly see in the rocks. Heck, with those three variables, I'd probably get it assayed asap.
Good luck! Hey, what area of TX? That will be a big clue!