Partial Petrification is an interesting status ailment with some unique properties. It doesn't actually do anything until the Petrification is full, at which point the status changes to permanent Petrification. The effects of Partial Petrification are cumulative, so 1/3 + 2/3 will result in full Petrification, as will any amount totaling at least 1. "Full" Partial Petrification means that the target will immediately be petrified, but it differs from normal Petrification in that you need resistance to Partial Petrification to prevent it.