Here is a guide to breed the gemstone dragons from May-December. All gemstone dragons have an incubation time of 31 hours. Keep in mind that getting a gemstone dragon has slim chances, but if you have the Epic Breeding Island, your chances increase. Also, Gemstone dragons cannot breed with any other dragons.

EmeraldDragon: (May) Crystal + Lichen

Pearl Dragon: (June) Snow + Seaweed

Ruby Dragon: (July) Chrome + Scorch

Peridot Dragon: (August) Crystal + Cactus

Sapphire Dragon: (September) Rain + Mountain

Opal Dragon: (October) Lava + Mud

Topaz Dragon: (November) Cactus + Firefly

Turquoise Dragon: (December) Poison + Swamp