You are looking at a pietersite skull, The skull is 5.1 inches long, from front to back. 

Please notice the the top of the skull. 

Pietersite was named in honor of its discovery by Sid Pieters. In 1962, Mr. Pieters was visiting a farm in Namibia, Africa, when he first laid eyes on a sample of this mineral. The stone appeared to be quite heavy for its size, so he took it to his workshop for further study. No sooner than had he cut the stone open, Pieters was stunned by the brilliant rays of his new finding. Mr. Pieters exclaimed, "Of all the gemstones I have seen in the world, this is one of the most beautiful." This stone has come to represent the movement and chaos that break up those energy patterns which are resistant to change. The energy of Pietersite is very forceful and jolts us into personal change. This stone represents change and indicates a need to make changes in your present life. In a lay-out place this stone on the solar plexus chakra, where the flow of energy leads to assimilation and integration.