Dwarves often brag about being descendants of mountain gods, and while that may very well be true your kind has been hewn from the very mountains themselves. Your skin is coarse and rough like granite, and has a greyish tint.
Like a boulder you are immovable, stubborn, and fixed rigid in your beliefs of justice and what is right as you ae in your assuredness of your kinds glorious creation.
Stone Skin. Once per day a stone dwarf can cause their skin to become thick and harden, becoming stone-like. They gain resilience against bludgeoning, piercing, and slashing damage for a number of 3 + Constitution modifier. While in this state the dwarf’s movement is reduced by 5’ and their weight is increased by 50 lbs. Your fists also harden like stone and deal 1d4+str damage. You can use your bonus action to make a second fist attack.
Stone Death. When a stone dwarf is dropped to zero HP they immediately become stone statue. While in this state the stone dwarf is not immune to damage at 0 HP rule (pg 197). The stone dwarf must still roll (and succeed) on their death saves to live. When the stone dwarf regains consciousness, or is healed to 1HP or above, they transform back to their normal form. Failure means that they permanently become a stone statue. The Hall of Kings of the stone dwarf kingdom is lined with the corpses of fallen heroes, permanently preserved.