Reminds me of the "glow rock" mentioned in http://www.imperial-library.info/interviews/skelm.shtml by the Khajiit that's near the Hall of Colossus.
Well I have read your bits - and there is no description of the various crystals mentioned. So they could be anything - but let's assume they are what was in the caves of Morrowind and other places there.
A lot of Skeleton man's interview is off the point - possibly intentionally so - so we know of the Halls of the Collossus and the radiation there nie? You think it could be crystals there are connected - maybe - suggesting that they are formed through the presence of concentrated magica/power - but then none of the Tribunal appeared to have them in their abodes (... not that they would have needed them.)
Thank you for drawing my attention to these fascinating topics, which I am sure will be most useful, [edit - non-essential content] The link mentions salt crystals too - no sign of magic crystals though ...
I did learn about Crystalisation in chemistry about - well longer ago than you've been around
I have not played Oblivion - I have no plans to do so - therefore unlike with the Lore of Morrowind and Daggerfall (plus part of Battlespire before that computer self-immolated itself), which I spent many, many fine hours with, I rely on the precociousness of people like you (most of whom joined these forums several years after I did) to bring me these tidbits on the new Lore - call it questing if you will. In this case none of the answers is really precisely informative , eh? Too bad.
Can anyone remember a cave in Morrowind that had the giant Crystals but no mages?
However the question of where soul gems come from 'nowadays' is still unanswered and no link between soul gems and these giant crystals is as yet forthcoming.
Re Welkynd Stones - they seem to differ in properties from the Morrowind ones. What I am wondering now is were the ones in Morrowind (if they are the same stones) tuned to power the Summon Daedra spells in so very many locations?
If yes then Daedra permanently found in various dungeon locations may be being summoned and held in place by this means - or maybe the stones power a reactivation of various summoning spells. That suggests that various mages and the Telvanni in Morrowind have mastered the ancient Ayelied discoveries. but there were no books on how to do this commonly available ...
There was a dungeon in the dungeons under a Fort in Morrowind that was full of Daedra - did they also had these great crystals?
Mind you I don't fancy carrying about a 15ft tall crystal whenever I go questing!
Soul Gems appear to be quite different in properties though - so I guess they are from a very different source - too bad.
Could the differrent kinds of soul gem each have their provenance in different Daedric realms of Oblivion, or are they imported from another continent?
Any other ideas?