This is a 5" long polished skull that was sculpted from green jade var. nephrite. The underside of the skull and the nostrils have been hollowed-out, making the specimen closer in resemblance to a real skull.
Jade is a silicate mineral that is best known for its green varieties, the most common of which are jadeite and nephrite. Jadeite is a variety of jade that's primarily composed of silicon, calcium and magnesium while nephrite contains silicon, sodium and aluminum. For thousands of years, jade has been used for ornamental purposes and as tools due to its relative strength and durability.