Rocks in a box

A wealthy Indian prince used to amuse himself with a little game.
He would show his visitors four identical boxes, lettered A to D as shown in the diagram, each containing a different precious stone.
He then presented his guests with a set of four clues, warning them that only one clue was true, the other three being totally false.
If they were able to work out exactly which jewel was in each of the four boxes, they would be allowed to keep the contents.

Could you have done so?


1 The diamond is in box B and the ruby in box D.
2 Box A contains the emerald but the ruby is not in box C.
3 The sapphire is in box two to the left of the one containing the emerald.
4 The ruby is in box B.

A starting tip?