A more thorough explanation:

The marketability test is a principle in mining law that requires a person to demonstrate that they can extract and sell a mineral from a mining claim on federal land at a profit. This test also requires that there is a large enough market for the mineral at the time of discovery to attract the efforts of a reasonably prudent person.

For example, if someone discovers a gold deposit on federal land, they must show that they can extract the gold and sell it at a profit. They must also demonstrate that there is a large enough market for gold to attract the efforts of a reasonably prudent person. If they cannot meet these requirements, they will not be able to obtain a patent on the mining claim.

Another example could be a person discovering a deposit of a rare mineral used in the production of electronics. They must show that they can extract the mineral and sell it at a profit. They must also demonstrate that there is a large enough market for the mineral to attract the efforts of a reasonably prudent person.

These examples illustrate how the marketability test ensures that mining claims are only granted to those who can extract and sell minerals at a profit, and that there is a viable market for the mineral at the time of discovery.