Hi,
Obsidian is one of my favourite stones. I wear a lot of it for protection and grounding and I have some wonderful pieces around my house and workshop too. It is a volcanic glass and there are many different 'feels' to obsidian depending on where it originates. The masculine Mexican Obsidian which is the easiest to get hold of, polishes up to a mirror like finish. When a mirror of this is used for scrying the results can be powerful and strong but is very sharp and clever in its energy, very direct and blunt and pointed, it can get straight to the bottom of the matter and show you the roots. Peruvian or Tibetan Obsidian is much softer and gentler and more female in her energy, she has a gentle silky sheen when polished and the visions are created in a subtler way, making sure you are eased into the seeing. The american Apache tear obsidian very rarely forms large enough pieces to be cut and polished as a mirror and because it is a true smoky obsidian the resulting polished sheet would not reflect an image anyway, so best used for their original purpose of protecting travellers, and keeping people safe
There are some other forms of obsidian, notably blue obsidian or electric obsidian, these are man-made glass and nothing like the natural aqua blue obsidian that rarely forms in ancient lava flows.