Path of the Rock

Some Barbarians tirelessly steel themselves to reach the peak in defense, not only training their body to reach a comparable toughness as stone, but calling forth actual stone or gems to use as shields and weapons.

Those Barbarians are extraordinary sturdy and difficult to deal damage to.

Especially, Earth Genasi Barbarians often follow this Primal Path.

Stone Shield

As you enter your rage, stones or gems grow out of your body or start hovering around you, protecting you from damage.

Starting at 3rd level, when you enter your rage you gain temporary hit points equal to twice your level in this class, plus your Constitution modifier.
While you are already raging, you can use another Rage to get this shield of half the temporary hit points. To get the full amount of temporary hit points again, you need to have spent at least one entire turn, not raging.

Stonefists

At 3rd level, you can cover your fists in stones or gems. While they are covered in stones, your unarmed attacks deal 1d4 + STR modifier bludgeoning damage on a hit.

The damage die increases by level, to a 1d6 at 6th level, to a 1d8 at 10th level and to a 1d10 at 14th level.

Impenetrable Fortress

Starting at 6th level, while you are raging, any damage against you, that isn't psychic, necrotic or poison is reduced by your Constitution modifier at a minimum of 1.

Rock Smash

At 10th level, you learn to shape the earth beneath you. As a bonus action, you slam a weapon, that deals bludgeoning damage or your fist into the earth beneath you, cracking the stone, making the area around you in a radius of upto 30 feet into difficult terrain for any creature other than you.
The weapon or fist that you used this feature with is covered in heavy magical rocks or gems as you pull it out. For the next minute that weapon deals an additional 2d8 bludgeoning damage and the weapon is considered magical if it isn't already.

Once you use this feature, you can’t use it again until you finish a short rest or long rest.

Unbreakable

Beginning at 14th level, your skin is so tough that the weak have trouble even scratching you and your mind is so disciplined that you are not easily fazed.

While you’re raging, when you take damage, you can use your reaction to attempt to block the damage. Make a Constitution saving throw. The DC equals the damage taken.
When you succeed the saving throw, you take no damage and you don't use up a charge for this feature. This will still count as damage done to you, required to maintain the rage per round.
You can use this feature up to two times and regain all expended uses left after a long rest.