Star Stone
From the Super Mario Wiki
The stone inside it's protective crystal.
The Star Stone is a special item used in Paper Mario. There is a place on Shiver Mountain where Mario has to find Madam Merlar, who has the Star Stone. She will give it to Mario to place inside a pedestal on the cliff wall. Once activated, it will create a huge staircase of ice and crystal for Mario to reach the Crystal Palace at the summit.
