The Mantle

The Aasimar, or “Sky-Born”, are the primary Dynast and Noble Houses of the Empire, and the Lirusyle Family . Most notably of course is the Aasimar's skin, appearing like polished stones and having a similar hard quality. Their eyes are crystalline, and those that grow hair (as many do not at all), it is more quill like. Even then, many wear wigs as fashion. These properties are assumed to be why they live such long lives, often around two centuries.
Tieflings, or “Earth-Born”, are very similar to their Aasimar cousins. They also sit among the many Dynast and Noble Houses in the Empire, but their stone-like skin is like smooth, unpolished stone. Their eyes are also crystalline, however instead of hair, a few Tieflings grow crystals from their head, often from afar looking like a crown, horns, or ornate jewelry.
Together the Aasimar and Tiefling are known as the Mantle, the original group birthed from the land itself when all plants and animals came to Erdon. The Eldren Fables, the oldest known stories recorded in stone, say the Mantle were formed out of the earth by the gods long before the Elves, Dwarves, and other races arrived.

Adults are medium sized, and both Aasimar and Tiefling gain +2 AC because of their stone skin, but have a max Dex of 14 as it hinders their movement. They gain advantage to Constitution saving throws.
Aasimar can heal twice as fast in rain, fog, or in clouds.
Tiefling can heal twice as fast while in contact with large, unworked stones or crystals.