Collectible coins encompass various types, including commemorative, bullion, and historical coins. Morgan Dollars, minted from 1878 to 1904 and again in 1921, are among the most sought-after U.S. coins, featuring a portrait of Liberty on the obverse and an eagle on the reverse. The 20 Twenty Dollar Gold piece, specifically the Liberty Head and Saint-Gaudens designs, serves as a significant example of U.S. numismatics, characterized by their historical value and gold content. The Philadelphia Mint played a crucial role in producing these and other collectible coins, contributing to their desirability among collectors.