This is something called a Far Infrared Thimble.
The little blurb accompanying the picture states:
"As the main materials of this far infrared thimble are high energy mineral and herbs from nature, the inside energy of this thimble can help to promote blood circulation for the tips of the nerve of the fingers. Meanwhile, it also can help the Qi Gone lovers to eliminate the foul Qi (or bad energy) inside the body by this far infrared thimble when they practice Qi Gone. Therefore, this is a very good product for multiple purposes." Well, that's good. Right?
The company that sells these wondrous thimbles, Qi Pao Enterprise Co., Ltd., also has teapots, eggcups, incense burners, and something called Gua Sha Boards that serve the same purpose. Great!