On Nirn (or at the very least in Tamriel), soul gems seem to be extremely common as they're found in almost any shop anywhere.
As I remember, the only source of new soul gems is the geode mining nodes in Blackreach.
Is this (and similar areas across Nirn) the sole source of soul gems in the world?
How come there are so many in circulation if they're only found in such remote locations (and seeing how they're destroyed upon use)?
Official quotes and sources much appreciated