Platinum Eagles are produced by the US Mint. They are .9995 fine (99.95% pure), and the 1-oz coins carry face values of $100. However, they sell for the value of their platinum content plus a small premium to cover the cost of manufacture and distribution.
Platinum Eagles were first minted in 1997, but when demand is low the Mint does not make them.
Although in some years the Mint has produced fractional-ounce Platinum Eagles, none have been made so far in 2014. Therefore, ½-oz, ¼-oz and 1/10-oz Platinum Eagles are available only when they show up in the secondary market.