It seems that this isn’t a stone, but a ray of Mirrow solidified by the midday heat, when the air in the land of the Genies is so blisteringly hot that it's hard to even breathe. An extremely valuable gem, which can only be found in the area around the mountain of Mystras.
There’s a very high chance of getting Mo-Datkhar of Nurid if you sift through 100 of this resource.