Whether you own both the minerals and the surface could depend simply on whether there was a mineral reservations in the deed where you acquired the property. If there was no reservation in your deed, then you received whatever mineral interest that was held by the owner you acquired from. But if your acquisition deed didn’t include any mineral reservation, the question then is whether all, or parts, of the mineral interest had been reserved at some point in the past.
Finding that answer could require checking the wording of every deed or other conveyance in the complete chain of title to the property. It would take researching at least as far back as required to establish that the full mineral interest had been reserved. If you confirmed that all, or some part, of the minerals were never reserved (or reserved for a specific time period that has expired) then the remaining mineral interest belongs to the current surface owner.