Rainbow obsidian is a stone that actually isn't a stone. It's glass that's formed within a volcano. When the volcano erupts, and the glass cools, it cools too quickly to become a crystal, therefore, glass.
Rainbow obsidian has a sheen, some can be quite bright. Mostly in shades of pink and green, the shades of the heart chakra, this Stone is wonderful for those of you who are going through a large, eruption- like change. Some types of obsidian are almost harsh in the way they heal, but not rainbow obsidian, probably because of its connection with the heart chakra and love. It's very gentle, and eases you through disturbing events, including breakups.