These  obsidian raven skulls are gorgeous. So perfect for protection on your altar.  Also great to meditate with for helping with prophetic dreams or visions. I like to use them in my work with the Morrigan. 
 
 Obsidian 
Keywords: Cleanse, Protection, Prophecy
Element: Fire
Planet:  Saturn/Pluto
Obsidian is formed by the quick cooling of volcanic lava in an earthly and scientific way that causes it to harden like glass. It has been around since the beginning of time and has been used in trading by the Mayans since 100 B.C.
 Black Obsidian Stone is a powerful cleanser of psychic smog created within your aura, and is a strong psychic protection stone. This stone has powerful metaphysical properties that will help to shield you against negativity. The energy of these stones may stimulate the gift of prophecy.