where can I find information on inherited mineral interest.

It is sometimes hard to get all the deed records figured out if you do not do it with regularity.  I suggest that you go to a large, well respected title company in your area and ask  them to do a "property profile" on the land.  (some companies call this search something else so yu may have to explain what you are looking for)  You will need the legal description. (They might even ask to see the will, but often it is not needed)  It will cost you somewhere about $100- depending on the complexity of the title.