You are looking at a Hematite skull ring.

Hematite is particularly effective at grounding and protecting. It harmonizes mind, body, and spirit. Used during out-of-body journeying, it protects the soul and grounds it back into the body. This stone has a strong yang element and balances the meridians, redressing yin imbalances. It dissolves negativity and prevents negative enegies from entering the aura, restoring peace and harmony to the body.