Crystal Collapse

How to play: the cavern holds four kinds of crystal. Tap any group of two or more matching crystals that touch — sideways or up and down, not diagonally — and the whole group shatters; everything above tumbles down, and an emptied column closes up. A group of n pays (n − 2)² points, so five crystals pay 9 where two pairs pay 1 apiece — the game is in growing big groups before you cash them. Hover to see what a group would pay. Shatter every last crystal and the clear pays a 1000-point bonus and the win; run out of touching pairs first, and the stranded crystals end the game.