I was looking at the description of the spell Creation in 5th Ed, and saw a gap. It lists the duration for "Precious Metals" but not for other metals. I thought it might be the same as stone and crystal, since they're mentioned together.
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.