Here is a list of all the jewels and its stats that you can get in the game...
Small Jewels: (Level: 1-45)

Small Diamond (
Defense +3)

Small Ruby (
HP +20)

Small Sapphire (
MP +20)

Small Emerald (
Attack +3)

Small Zircon (
Block +2%)

Small Black Pearl (
Attack Rate +3)
Big Jewels: (Level: 35-60)

Big Diamond (
Defense +5)

Big Ruby (
HP +30)

Big Sapphire (
MP +30)

Big Aquamarine (
MP +2%)

Big Emerald (
Attack +5)

Big Zircon (
Block +3%)

Big Topaz (
HP +2%)

Big Black Pearl (
Attack Rate +4)
Fantastic Jewels: (Level: 50-94)

Fantastic Diamond (
Defense +7)

Fantastic Ruby (
HP +50)

Fantastic White Pearl (
Resistance +3%)

Fantastic Sapphire (
MP +50)

Fantastic Aquamarine (
MP +3%)

Fantastic Emerald (
Attack +5)

Fantastic Amethyst (
Skill Block +3%)

Fantastic Zircon (
Block +5%)

Fantastic Topaz (
HP +3%)

Fantastic Black Pearl (
Attack Rate +6)