Obsidian XXL. Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. In the same time it stops any evil or negative energy even before it get any hold on you or anyone you love. This is the most important crystal for grounding, that helps you to stay firm and strong no matter what. Just like in geology, obsidian is the foundation, starting point of everything.