Barbarians who walk the Path of Seismic Strata manifest the unstoppable weight and density of the deep stone when their rage takes hold. As they master this internal connection, they eventually develop the sensory and burrowing adaptations of deep-earth denizens.
In combat, these warriors undergo a physical, geological transformation. Their skin calcifies, their fists become crushing boulders, and they move through the battlefield with the inevitability of a tectonic shift.
Your body adapts to the groundedness of primordial earth. Your physical weight doubles, and you have Advantage on any saving throw made to resist being pushed, pulled, or knocked to the Prone condition.
You are unaffected by Difficult Terrain composed of rubble, dirt, rock, mud, or similar earthen materials.
Additionally, you have an intuitive ability to speak, read, and write Primordial (Terran).
When you enter your Rage, you draw the grinding inevitability of the earth onto yourself, becoming encased in rocky protrusions. You gain the following benefits while Raging:
Hardcase. When you activate your Rage and at the start of each of your turns while Raging, you gain Temporary Hit Points equal to your Rage bonus plus your Proficiency Bonus.
Rocky Fists. Your Unarmed Strikes deal 1d12 Bludgeoning damage on a hit. For the purpose of your Weapon Mastery features, you can treat your Unarmed Strikes as weapons that have the Topple mastery property.
Tremorsense. You gain tremorsense with a range of 60 feet.
Find. You can pinpoint the scent of precious metals and gemstones within 60 feet of you.
Consume. As a Magic Action, you consume a handful of nonmagical gemstones and precious metals (one or more objects) to restore your vitality. The consumed objects are destroyed, and you regain 1 Hit Point for every 5 gp the objects were worth (round down). If the objects were worth at least 50 gp, you also regain a usage of your Rage. Once you have used this ability, you must finish a Short or Long Rest before you can use it again.
When you can choose a Brutal Strike effect and both you and your target are standing on the ground, you have the following additional effect option:
Seismic Strike. The ground beneath your target vibrates violently until the start of your next turn, in a 10 foot Emanation that only affects targets on the ground. Whenever a creature enters the Emanation or starts its turn there, it must succeed on a Strength saving throw (DC 8 plus your Strength modifier and Proficiency Bonus) or take Bludgeoning damage equal to your Proficiency Bonus and gain the Prone condition. You are not affected by Emanations created by this effect, nor are creatures that have the Elemental (Earth) creature type.
You have Resistance to Bludgeoning, Piercing, and Slashing damage, and tremorsense with a range of 60 feet all the time now, not just while Raging.
Elemental Affinity. You gain the creature type of Elemental (Earth) in addition to your other creature types, and you suffer no ill effects from the environment of the Elemental Plane of Earth. The initial disposition of Earth Elementals towards you is one category better than it normally would be, and they will not attack you unless their disposition changes to hostile. However, the initial disposition of Air Elementals towards you is one category worse than it normally would be.
Earth Meld. You gain a Burrow Speed equal to your Speed. You can burrow through unworked earth, solid rock, and stone without disturbing the material you are moving through. Additionally, you can take a Short or Long Rest while completely submerged in earth or stone, without needing to eat, drink, or breathe.