Because you are made of rock, you are naturally hard to damage. Your AC is 17+con modifier. Your hit point maximum increases by 1, and it increases by 1 every time you gain a level.

Due to your round exterior you can be rolled by anyone with a strength score of at least 14 without penalties on their movement

Due to being unable to speak normally you have telepathy instead up to 60 feet

You have disadvantage on dexterity saving throws and checks due to being unable to move. You do though have advantage on saves and checks against being moved or grappled against your will.

While anyone is behind you they are considered to be in full cover

You cannot move or wield items of any kind due to having no limbs.