The Rings of Akhaten was an asteroid belt around the sentient planet Akhaten. The asteroids were composed of solidified molten magma ore fragments.
The oxygen-dependent human Clara Oswald was able to breathe in the Rings of Akhaten. This suggests that the atmosphere of Akhaten was either very large, or was modified by other life-forms in order to make it habitable.
The inhabited asteroid Tiaanamat was built on the largest piece of ore on the outer ring as a docking point. Many species from across the universe inhabited Tiaanamat, and both sold and purchased rare and exotic goods in vast winding markets.
Tiaanamat played host to the Festival of Offerings, a millennial choral ceremony held when the Rings aligned. It was a huge event, in which species from across the system of the Sun-singers of Akhet gathered to watch.
Within relatively close proximity of Tiaanamat was the Pyramid of the Rings of Akhaten. This was a pyramidic temple for the Old God, and was located on an small asteroid. The Pyramid was a holy site for the Sun-singers of Akhet. They believed that all life in the universe originated there. (TV: The Rings of Akhaten)