The following is a list of Gems (weapon attachments that take one space but do multiple things) and what each does.

Amethyst: +10 Mage, +10 Dino, +10 Ice
Aquamarine: +10 Sea, +10 Flying, +10 Ice
Diamond: + 5 vs. All Creatures, Extra +5 vs. Steel
Emerald: +10 Dino, +10 Plant, +10 Magic
Garnet: +10 Animal, +10 Rock, +10 Fire, +5 Attack
Opal: +10 Mage, +10 Steel, +10 Endurance
Pearl: +10 Undead, +10 Thunder, +10 Endurance
Peridot: +10 Plant, +10 Animal, +10 Holy, +5 Attack
Ruby: +10 Mimic, +10 Fire, +10 Speed
Sapphire: +10 Flying, +10 Wind, +10 Magic
Topaz: +10 Undead, +10 Flying, +10 Speed, +5 Attack
Turquoise: +10 Rock, +10 Mimic, +10 Ice