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Obsidian - Black
Source: Mexico, volcanic regions
Chakra: Base
Zodiac: Sagittarius
General: Having no crystalline structure, Obsidian has no boundaries or limitations, working extremely fast with great power.  Obsidian’s greatest gift is insight into the cause of disease.  Mercilessly exposing flaws, weaknesses, blockages, and disempowering conditions, nothing can be hidden.  Impelling growth, it lends solid support but needs careful handling and is best used under the guidance of a qualified therapist.  Providing deep soul-healing, Obsidian goes back to past lives to heal festering emotions or trauma carried forward into the present, bringing depth and clarity to emotions.  A strongly protective stone, Obsidian forms a shield against negativity, providing a grounding cord from the base chakra to the centre of the earth.  It absorbs negative energies from the environment and blocks psychic attack and negative spiritual influences.  Obsidian brings clarity to the mind and clears confusion and constricting beliefs but makes it absolutely clear what lies behind mental distress or disease.
Black Obsidian, in addition to carrying the generic properties of Obsidian, this shamanic stone removes disorder from the body and powerfully draws off negativity and repels curses.  Grounding the soul and spiritual forces into the physical plane, Black Obsidian brings them under the direction of the conscious will.  Black Obsidian forces facing up to one’s true Self, taking you deep into the subconscious mind, magnifying negative energies so that they can be fully experienced and released.  This healing effect can work on the ancestral and family line.  Reversing previous misuse of power, Black Obsidian addresses power issues on all levels.
Beneficial For: Compassion, strength, digestion of anything that is hard to accept, detoxification, blockages, hardened arteries, arthritis, joint pain, cramp, injuries, pain, bleeding, circulation, enlarged prostrate, and warming the extremities.1
Emotional Healing: Emotional healing after trauma of any kind.  Good for victims of sexual assault.  Assists in expressing grief that is blocked especially in children.  A small Obsidian sphere in your workspace and at home absorbs free-floating irritability and restlessness. 
Practical Uses: Protective when carried or worn as jewellery if others offload their problems on to you or make excessive demands on your time.
Workplace: Ornamental small Obsidian arrows in your workspace facing outwards protect you from gossip or spite.2
References:
Judy Hall, “The Encyclopedia of Crystals”, Bounty Books, London, 2015
Cassandra Eason, “The Complete Crystal Handbook”, Sterling Publishing, New York, 2010