Rare drop while Mining. Can be found in Sunken Chest, Hidden Cache, Dream Chests. Sold by the merchant Deviaran.
There are the following types of Gems: Turquoise, Sunstone, Obsidian, Fire Opal, Jade, Amber.
Amber becomes available when a mining mentee reaches the 5 star rating.
Gems are used in Crafting for rings, in Alchemy, in Carpentry for speciality chests. Amber also needs in Enchanting for Primeval token.
Jade are most rarely type, used for Top Secret Tools(last one in 2nd tree of Teachings) and ring in Crafting.