Granite Chest

The loot pool is the plain gold chest one, so a granite cabin is another roll at a Magic Mirror or a Cloud in a Bottle and nothing tied to the biome. That is still reason enough to sweep every cabin you pass, because granite caves are hostile enough that most players walk around them and leave the chests sitting.

The container itself is worth mining out. Granite furniture has one of the sharper looks in the game and crafting a matching set is slow compared to pocketing the ones the world already made. Empty it first: a chest with anything left inside will not come up.