I am playing as a sword and shield fighter, and I am debating on using the Atronach stone. I never use magic at all so I dont care about the stunted magicka regeneration rate but thought that the 50 pt spell absorption might be useful.

Question:
1.) Will it still absorb magicka if my magick bar is full? (since I never cast?
2.) Does it work by negating 50 pts of the damage or does it negate it all 50% of the time? Like how does it work exactly beyond just what I think it does.

Works if magicka is full, and absorption is all or nothing, unlike resistance which is % damage mitigation.

On a related note that won't really help the OP, it's bad for Conjurors because it occasionally makes you negate your own summons

Alright, thanks guys. I prefer not to leave it up to chance so I am going to just go back to my beloved Lady Stone.

If you want reliable magic resistance, Lord is your best bet, 50 armour (that only translates to 6% less damage though) and 25% magic resistance.