These are gorgeous and the quality is just perfect 10cm diameter with a 1cm thickness these come with a stand too.
Known as an Obsidian Scrying Mirror,  
Scrying is a form of divination involving gazing into a blank surface such as a mirror, and was first introduced into Europe around 16th century when Spanish Conquistadors returning from Mexico brought back ritual mirrors looted from the Aztecs.
Obsidian mirrors were closely associated with the deity Tezcatlipoca, whose name translates as “Smoking Mirror.
The use of mirrors in Mesoamerican culture was associated with the idea that they served as portals to a realm that could be seen but not interacted with.
Early mirrors were fashioned from single pieces of iron ore, polished to produce a highly reflective surface.
An ancient tradition among many Mesoamerican cultures was the practice of divination using the surface of a bowl of water as a mirror.
Obsidian is a protective stone which is also said to ground any spiritual energy and dissolves worry and fear, which are helpful qualities when a person wants to work with divination of any kind.

Obsidian Black Mirror