I have studied obsidian for many years. Obsidian is an igneous rock and is currently mainly used to make Feng Shui mascots. However, there are many kinds of obsidian materials. The more common ones are black gold obsidian, rainbow-eyed obsidian, and golden obsidian.
Judging from the picture you sent, this is a piece of black gold obsidian, also called pure black obsidian stone. It is real. The inside of the obsidian is light-transmissive and appears yellow. Feel free to wear it!