Black Obsidian is a type of volcanic glass that is formed when molten lava cools quickly aka "Dragon Glass" for my fellow GoT fans. This crystal skull is the perfect tool for psychic protection, shielding and grounding to Mother Earth.
Like all crystals, there are many, many more uses than I can include here and I encourage you to do a quick search on your own for more information.
*Crystal healing and other types of energy tools such as Orgone are not to be considered as a substitute for conventional medicine. If you have a serious health issue, you should consult your doctor.