Nasu aka Nasa (Zoroastrianism) and Tower of Silence
Nasu (Also; Druj Nasu, Nasa, Nas, Nasuš) is the Avestan name of the female Zoroastrian demon (daeva) of corpse matter. She resides in the north (Vendidad.
A Survey of Birds and Fabulous Stones
Christopher J. Duffin (2012): A Survey of Birds and Fabulous Stones, Folklore, 123:2, 179-197 http://dx.doi.org/10.1080/0015587X.2012.682477 Summary: The records of fabulous stones