Which $1 coin is rare?

Excuse me, could you please elaborate on the question about the rare $1 coin? Are you referring to a specific type of coin issued by the U.S. Mint, or perhaps a rare coin from another country? Additionally, what era are we considering when discussing rarity? It would be helpful to have more context to provide an accurate answer. For instance, some rare $1 coins in the United States include the 1916-D Mercury dime, which is a rare variety of the dime, or the 1907 Ultra High Relief Saint-Gaudens double eagle, which is an extremely scarce $20 gold coin, but not technically a $1 coin. Clarifying these details would allow me to give a more precise response.