I've discovered a way to reproduce the cubes! I am playing with Ak'shel and was passing through the third floor of the white tower. I was thinking it was just too dull to have the cube in the cursor, then I placed it as a weapon on his hand. When first I used the cube, it appeared in the cursor again! But other cube remained at Ak'shell's hand! Now I have two cubes!
Escape the dark halls
To escape the Dark Halls click on the top of the crates to open them Put them under a window with a crack in it, in the room that has the purple sphere in the middle. Change your magic to spark. Stand back and use spark. After several times you should destroy the sphere and go out the window with the exit at the end.