Rising Gems is on a 5x5 reel. When you rotate the reels on Rising Gems, you will notice that not all spaces are full of symbols. Although it does make the game look sparse, Rising Gems still wins frequent victories.
To get a winning combination, you must place three or more symbols in a group - touch the top/bottom sides. You can even get 16 types of victory combinations (and more), the most generous of which comes from the clown symbols, which give you a 700x bonus.