Line 3; Most real estate brokers are not familiar with the status of title to the mineral interests, the specific clauses that may be important to a party who desires to retain or convey mineral interests, or the value of mineral interests or mineral leases. Such transactions may require the neogotiation of complex legal clauses to accurately reflect the rights and obligations of the paries. Real estate brokers and salespersons are not attorneys and may not engage in the unauthorized practice of law. (this is just a partial reading of Information About Mineral Clauses in Contract forms.
I would definetly get legal advice from a Mineral Rights attorney.
If you are talking about a single unit being sold, then the seller may have never owned mineral rights to begin with. They own the space in which they inhabit and a percentage of common areas. It is likely that the condo developer holds any mineral rights, or has passed them on to the owners in equal portions which may be bound to the land.
This part of Real Estate can be confusing and very inconsistent. I would check the deed.