You searched for: “petrifier
petrifier (s) (noun), petrifiers (pl)
1. That which causes an object to become obdurate or a person to become insensitive and unresponsive: Dissolved minerals are petrifiers which can change plant material into a fossilized form, but only after an exceedingly long time!

A very strong fear of heights can be a petrifier for some people causing them to be completely paralyzed during the experience.