Coyolxauhqui was the moon goddess according the Aztec mythology. Her name means Golden Bells. She was the daughter of the earth goddess, Coatlicue, and the sister of the Sun god, Huitzilopochtli.
These 50 pesos coins are made of copper-nickel, so they are worth very little when in circulated condition.
Typical catalog values for the 50 Pesos are:
worn: less that $1 US dollar approximate catalog value
average circulated: $1
well preserved: $2.5
fully uncirculated: $5