Maryland Code, Environment § 15-1201

(1) Gas;

(2) Oil and oil shale;

(3) Coal;

(4) Gaseous, liquid, and solid hydrocarbons;

(5) Cement materials, sand and gravel, road materials, and building stone;

(6) Chemical substances;

(7) Gemstone, metallic, fissionable, and nonfissionable ores; and

(8) Colloidal and other clay, steam, and geothermal resources.

(f)(1) “Surface owner” means any person vested with a whole or undivided fee simple interest or other freehold interest in the surface estate.

(2) “Surface owner” does not include the owner of a right-of-way, easement, or leasehold on the surface estate.

(g)(1) “Unknown or missing owner” means any person vested with a severed mineral interest whose present identity or location cannot be determined:

(2) “Unknown or missing owner” includes the heirs, successors, or assignees of an unknown or missing owner.