CRYSTAL THOUGHT CONDENSER
A spectator selects a card from an ordinary deck. The performer displays a small solid crystal cube, which he explains will condense and focus thought rays, just like a lens focuses light rays.
The cube is held between finger and thumb, right under the spectator's nose, and being completely transparent, the spectators can see there is nothing in the cube. The spectator is asked to concentrate intently on the selected card as the performer moves the cube forward and backward, twisting it to bring it in focus. Suddenly an image of the selected card appears in the centre of the cube, and it can be clearly seen by the spectator. Then, just as suddenly it vanishes, and you can then toss the cube out for examination.
You could also make the image of a selected number, word, or design appear in the cube.