In the spell description these are referred to together as "mineral objects":
You can also use this spell to create mineral objects such as stone, crystal, or metal.
And, according to here, "Precious Metals" are the types used in currency (for 5e this includes platinum, gold, electrum, silver, copper).
Due to the description lumping of "stone, crystal, or metal" together, non-precious metals should be within the "Stone or Crystal" 12 hour duration category.