Have any coins meant to be spent for their face value (as opposed to bought up by collectors and hoarded) been made largely of platinum, to the point where any other metal could be seen as merely an additive? (For example, gold coins are not 100% pure gold. They are gold with a few relatively incidental additives.)
If not, why not? (“It’s too expensive” doesn’t quite work. Gold is pretty expensive as well, yet many nations have minted gold coins meant to be spent at face value.)
I know this is actually excluded from your criterion that they are “meant to be spent for their face value”, but there are American platinum proof coins (you might already be aware of this, I don’t know). While I can’t imagine anyone would spend them for their $10 to $100 face value, they actually are legal tender.
http://www.usmint.gov/mint_programs/american_eagles/index.cfm?action=American_Eagle_Platinum_Proof
Beyond that, I gotta admit I really don’t know. Wikipedia mentions, “Platinum coins are an old form of money” but gives no examples:
http://en.wikipedia.org/wiki/Platinum_coin
I expect samclem will probably know something more.
Oh yeah, those. I knew about those. You’d have to be pretty kooky to try and spend them at face value, however. You’d have to be … political candidate kooky. 
And they are excluded, technicalities on the meaning of ‘legal tender’ aside. Obviously, nobody at the Mint expects anyone to spend those babies at face value.
Russian platinum coins. Issed by Russian Empire, USSR, and modern republican Russia
Very interesting. Thank you.
The Russian platinum coins issued from 1828-1845 or so were indeed actual circulating coins. Not that they were used all that much in commerce. Probably just used in transactions where quite a bit of money was needed. I think the higher denomination platinum pieces of the time, the 6 rubles and the 12 rubles didn’t circulate.
There are NO other platinum coins that I can think of the actually circulated.