How do you breed a sapphire dragon in DragonVale?

The sapphire dragon is a limited edition gemstone dragon. It is only available in the month of September. You cannot breed gemstone dragons together to make other gemstone dragons, and they must live on the gemstone island. They produce gems instead of coins. You can get a maximum of one gem a week per gemstone dragon.

Some successful combinations for breeding are:

Mountain + Rain (most successful at 12%)

Steel + Storm

Mountain + Water

Mud + Evergreen

Bloom + Crystal