Grimrock

I am in crystal mines. It looks like I have done all. Now I am in 2nd floor and in the north west part I need another mines key. Any clue where they are ?

I stand in front of the door where you have to solve the ROCK SWORD SCROLL riddle. I managed to do that without help. But when I turn back - I can see a green gem above. Any clue how to get to there ?

I just found out how to cast spells with none spellcasters. I found a sword that could cast fireballs. To use it, I had to give my rogue 1 point in concentration. After that he was able to use a caster ORB that also needed conceantration 1. Once the Rogue wear the orb and you click on it he does not...