Your patron is a noble dao or Ogremoch, the evil Prince of Elemental Earth.

Greedy, malicious, miserly and contemptuous describe all elemental earth patrons. While they may seem slow to judge, their punishments come swift and weighty  so any warlock walking this path must tread lightly lest they raise their patron's ire. If you are looking for a kind and beneficent patron look elsewhere, for this type of patron never has those traits. Some are demanding, some may intimidate you into a pact, but their overall goal is always self-serving avarice.

Special Pact Conditions

These patrons are at odds with the powers of the Elemental Plane of Air. You are charged with destroying any denizen of that plane you come across. (Killing air genasi is not required, but may gain you some favor with your patron.)  You are further charged with the freeing of any denizen of the Elemental Plane of earth that is bound by mortal magic and the slaughter of those who dare to cast such bindings as summon elemental. You are especially charged with the destruction of golems to free their captured elemental spirits, any tomes for the creation of such, and the speedy execution of those who enslave or control earth elemental spirits in such a manner. While not specifically charged to do so, you are expected to gift your patron a steady supply of gifts-gems are always well accepted and quality slaves are appreciated by Dao.

Binding Mark

Your skin begins to calcify. The calcification expands across your face and body till it completely covers you at level 20. This calcification has no effect on movement or armor class, it is merely cosmetic.

 Pact Boon

Pact of the Chain: your familiar is a magma mephit or a mud mephit.

Pact of the Blade: your pact weapon is silvered adamantium.

Pact of the Tome: your book of shadows manifests as a smoky quartz crystal ball. When you gaze upon it, you can see your spells written in the inclusions in the crystal.

Pact of the Talisman:  a 5 pound stone of pure elemental basalt from the Elemental Plane of Earth. Whomever bears the Talisman has resistance to bludgeoning, piercing and slashing damage and advantage on saves vs petrification.

Expanded Spell List

You learn mold earth as a warlock cantrip which does not count against your warlocks cantrips known. Your Earth Patron also lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Earth Patron Expanded Spells

SPELL LEVEL	SPELLS
1st	catapult, earth tremor
2nd	earthbind, Maximilian's earthen grasp
3rd	erupting earth,meld into stone
4th	stone shape, stoneskin
5th	transmute rock, wall of stone

Grounded

You learn Terran, the primordial language of earth.

You ignore difficult terrain.  At 6th level you save at advantage vs effects that would move you or knock you prone.  At 10th level you become immune to effects that would move you or knock you prone.

Call Elemental

Starting at 6th level, you can call for an earth elemental with HD equal to half your level (round up) to come to your aid once between rests. 

The elemental makes a wisdom saving throw vs your spell save dc. If successful, no elemental answers the call.  Otherwise, the elemental appears in the nearest open space close to you, is friendly to you and acts immediately after you in the round. The elemental remains a maximum number of rounds equal to your Warlock spell save dc, or until you thank and dismiss the creature as a free action. 

Frequent usage of this feature, or if called elementals are abused by you or your allies will cause future callings to be less likely to succeed. (Saves vs this feature will be made at advantage.)

Stone's Resistance

At 10th level you gain Stone's Resistance; you have resistance to bludgeoning, piercing and slashing damage and save vs petrification at advantage. If you otherwise have these resistances or save advantage vs petrification, you gain immunity to these damage types and/or condition instead.

Elemental Form

Starting at 14th level, as an action, You can expend a pact slot to transform into an earth elemental. All equipment carried, worn or wielded transforms with you.

You can maintain the transformation without concentration a number of minutes equal to your level on the prime material plane, indefinitely on an elemental plane or a number of rounds equal to your level on any other plane or demi-plane.

You may end the transformation as a free action and it ends automatically if you are killed.

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