Smoky Obsidian, also called Apache Tears, is one of the best stones for grounding and clearing negativity. In this respect I regard them as second best only to smoky quartz. At first glance it can be hard to tell smoky and black obsidian apart, but if you hold one up to the light you will be able to see through smoky obsidian, but not through black. You may also discover that some are banded or layered, which can make these particularly useful for getting to the root of problematic or difficult situations. Smoky obsidian can also be useful in energy field protection, creating a "smoke screen", rather than the mirror of the other obsidians. Even so, they can help one hide or shield one's energy field if there is a need.