As used in this Act the following definitions shall apply:
(a) A "severed mineral interest" is any whole or fractional interest in any or all minerals which have been severed from the surface estate by grant, exception, reservation or other means.(b) An "unknown or missing owner" is any person or entity vested with a severed mineral interest and whose present identity or location cannot be determined from the records of the county in which the severed mineral interest is located and by diligent inquiry in the vicinity of the owner's last known place of residence, and shall include his unknown heirs and his unknown successors and assigns.(c) A "surface owner" is any person or entity vested with a whole or undivided fee simple interest or other freehold interest in the surface estate overlying a severed mineral interest but does not include an owner of a right of way, easement, leasehold or any other lesser estate.