Jewels can only be swapped if after the swap there are at least 3 or more same shape or color in a row or column. Otherwise the jewels return to their original position. There is a clock shown on the left. When it counts down to 0 the game is over. The high scores are stored in $HOME/.jewelscores
Hit spacebar to start a new game then select the difficulty number by pressing '0', '1', '2', '3' or '4'. You can always press 'ESC' to exit. During playing press 'p' to pause the game.
The code is a conversion of Dave Ashley's C program (GLjewel) to Scheme with some modifications and enhancements.