I was at Michael's Craft Store earlier today because I was getting some terracotta pots and I found these:
They're glass cut to look like gems! 5 dollars, but worth it if you really like that sort of thing. If you do decide to get these, then make sure you get the GLASS ones and don't get the ones covered with silver colored paint because they contain lead, which will slowly poison your fish. The glass ones contain no lead and are completely fish safe. (Cali passed a prop. that requires all items containing lead to plainly state so on their packaging.)