Related Clues:

• Artist's medium
• Valuable rock
• Manet medium
• Rock with potential
• What some seams are made of
• ... and its product
• It may pan out
• Loosen up, maybe
• Miner's bonanza
• Galena or mispickel
• Olive or corn follower
• Hematite, e.g.
• German preposition
• Vein contents, perhaps
• Bauxite or galena