The Horns of Nimon
Aneth was the home planet of the Anethans and was ruled by a monarchy. Hymetusite could be found on Aneth. It was subject to the Skonnan Empire until the empire collapsed. Several generations later, the Skonnans returned, demanding sacrifices of people and hymetusite, both of which were given as sacrifice to the Nimon.
The Fourth Doctor said he had visited Aneth at some undisclosed point in time and considered it a pleasant place. (The Horns of Nimon)