INDEX FINGER, typically reserved for affiliation rings (fraternal, familial, membership crests). Associated with power, assertion, authority and the planet Jupiter. While tin is the associated metal, most commonly bright silver rings are worn.
FOURTH FINGER, usually reserved for wedding or engagement rings (more typically on the left hand, but acceptable on the right). Non-wedding rings worn on this finger tend to be silver. Associated with the moon, romance, creativity and beauty.