Obsidian is an igneous rock that is made from high silica magma, and cools so fast that it is unable to form crystals! Obsidian is often referred to as volcanic glass. -- Kate Borden Note the glassy conchoidal fracture pattern.
A rainbow obsidian heart is a wonderful crystal to use to nurture and rejuvenate your heart after experiencing an emotional trauma, such as a broken heart or period of grief. Lay the rainbow obsidian heart over your heart, with the he