One of my favorite powerful crystals to effectively release blocks caused by traumas. Obsidian is actually glass formed from volcanic lava that hardened so quickly it formed no crystalline structure.
Obsidian is usually seen as intense because it works rapidly at giving you insights to your shadow self; your weaknesses, fears, flaws, etc. Deep soul healing is not always an easy task, but Obsidian will help protect you through the darkest times. Obsidian has long been used as a scrying tool during trance work.
There is a belief that mirrors serve as portals to other realms or planes of existence that can be observed but not interacted with it. Obsidian scrying mirrors were used for this purpose, especially in rituals pertaining to self reflection. This mirror can be used for its protecting qualities to clear your space and ward off negativity.