Quarter

The variant of ancient US Quarter coin that John and Dr. Halsey flipped.

A Quarter is an ancient coin used by the 20th-21st Century US government as part of its national currency. Equivalent to 25 Cents, under the United Earth Government the currency was discontinued in favor of the UN Credit, and Quarters have become valuable antiques, but have no value as currency anymore.

One side of a Quarter bears an image of ancient US general and president George Washington, while the other side bears an Eagle, the national symbol of the US. Dr. Elizabeth Catherine Halsey brought one with her while testing Master Chief a potential candidate for the Spartan II Program, flipping it to test whether he could accurately predict the outcome. As a reward for guessing correctly, she allowed him to keep the coin, and the eagle became the symbol for the Spartan II's.

Because the Eagle side was replaced with a unique image for each state in 1999, this means that the coin used by Halsey must have been minted prior to then, giving the object an age of at least 518 years.