Coins specifically listed in the Internal Revenue Code and minted by the United States. These include:

American Gold Eagles: minted in 1/10 ounce, 1/4 ounce, 1/2 ounce and 1 ounce coins. These have fineness of .917 to .999. Please note only American Eagle Coins with .917 fineness are allowed. Any other coin from any other country must be of .999 fineness or higher.

American Gold Buffalo coins: first minted in 2006, they are .9999 fine (know as four nines or quad nines). Note that the specially processed proof version of this coin is NOT acceptable due to the treatment raising the value of the coin beyond the value of the metal. This coin is not accepted by some trustees in any version.

American Silver Eagles: silver eagles are minted in only one form, as a 1 ounce coin. They are of bullion finess, but are only .999 (three nines) due to the addition of copper for added durability.

American Platinum Eagles: minted in 1/10 ounce, 1/4 ounce, 1/2 ounce and 1 ounce coins. These have fineness of .9995. 

In addition to these American coins, there are some coins issued by mints of other nations that meet the fineness requirements:

Australian Nugget Kangaroo Gold Coins: .9999 fine

Australian Nugget Kangaroo and Kookaburra Silver Coins: .999 fine

Australian Nugget Koala Platinum Coins: .9995 fine

Austrian Philharmonic Gold Coins: .999 fine

Austrian Philharmonic Silver Coins: .999 fine

Canadian Maple Leaf Gold Coins: .9999 fine

Canadian Maple Leaf Silver Coins: .9999 fine

Canadian Maple Leaf Platinum Coins: .9995 fine

Canadian Maple Leaf Palladium Coins: .9995 fine

Mexican Libertad Silver Coins: .999 fine (not allowed by some trustees)

Isle of Man Noble Platinum Coins: .9995 fine (not allowed by some trustees)

If the above coins have been graded for condition by certification organizations and placed in tamper-proof plastic containers called “slabs”, they will generally fall into the collectible category and will not be allowed for IRAs.