Traditionally mined in Austria and Pakistan, emeralds are a type of the mineral beryl which have their green colour on account of chromium and/or iron. Generally emeralds have a higher number of inclusions than say diamonds, thus they are not as strong and so more likely to become damaged.
This particular stone is set in a white gold ring (except the claws in yellow gold) encased with small diamonds so as not to take away from the beauty of the stone itself. Note the selective focus on the claw grasping the stone. This emerald was mined in Colombia and with this setting costs the same as the average house price in London., UK