Oh boy. You could write a book on mineral rights in Texas. Just kidding - it could fill a library.
If you’re interested in knowing more about what your family might own and how this works, happy to take some educated guesses. Just let me know if you’re interested, and I can pose a few general follow up questions to narrow it down. Smart of your great-grandparents though - my west Texan forebearers never retained any mineral rights lmfao.
By the way, for what it’s worth, Texas’s public university systems are in large part funded by state-owned mineral rights in West Texas which includes a little oil field called the Permian Basin. As a result, UT’s endowment is either comparable in size, or perhaps now larger than, Harvard’s famously large endowment (that’s what she said?). Obviously smaller on a per capita basis, but definitely the mineral resources of Texas do fund some public goods.
Final comment - I can still hear a quote from some game on unlocking part of the tech tree (Civ VI? Alpha Centauri?): “The meek shall inherit the earth - but not its mineral rights.”