Help me remember the name of this fiction book?

I just remebered a book i read when i was about 6 (roughly 12 years ago). it was about these sister pricesses that all ruled a jewel kingdom of their own. ruby, emerald, diamond, etc. and they each wore a crown with their jewel on it. there was a master crown with all the jewels on it that an evil woman stole and they had to use the power of their jewels to get it back. the cover was blue i think. it had pictures of each oth the princesses in their golden towers on the cover, and pics with descriptions on the back. it wasent a very long book. does anyone know? thank you.