A "dollar" is a dollar. It is the measure. Like an inch.

It does not matter what the coins are made of or how big or small they are or aren't.

All the matters is they are authorized to be minted by statute.

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What dollar or cent amount is stamped on it as specified in the statute.

If you want to spend a $50 dollar gold coin it will be accepted for $50 of legal tender.

If you want to spend a $1 silver eagle it will be accepted for $1 of legal tender.

Of course both of those actions would be galactically stupid. However if you wish to transact in gold or silver coin that is your choice and I'd would be happy to do business with you.

Clear?