In this subtitle the following words have the meanings indicated. “Mineral” includes: Gas; Oil and oil shale; Coal; Gaseous, liquid, and solid hydrocarbons; Cement materials, sand and gravel, road materials, and building stone; Chemical substances; Gemstone, metallic, fissionable, and nonfissionable ores; and Colloidal and other clay, steam, and geothermal resources. “Mineral interest” means an interest in a mineral estate, however created and regardless of form, whether absolute or fractional, divided or undivided, corporeal or incorporeal, including a fee simple or any lesser interest or any kind of royalty, production payment, executive right, nonexecutive right, leasehold, or lien in minerals, regardless of character. “Severed mineral interest” means a mineral interest that is severed from the interest in the surface estate overlying the mineral interest. “Surface estate” means an interest in the estate overlying a mineral interest. “Surface owner” means any person vested with a whole or undivided fee simple interest or other freehold interest in the surface estate. “Surface owner” does not include the owner of a right–of–way, easement, or leasehold on the surface estate. “Unknown or missing owner” means any person vested with a severed mineral interest whose present identity or location cannot be determined: From the records of the county where the severed mineral interest is located; or By diligent inquiry in the vicinity of the owner’s last known place of residence. “Unknown or missing owner” includes the heirs, successors, or assignees of an unknown or missing owner.