Obsidian is a natural glass of volcanic origin. This cabochon shows deep chocolate brown bands along the bottom which contrast nicely with the deep dark background.
Looks like a empty field on a moonlight night.

The back is natural.

The first picture shows the stone slightly back lit to show how the dark area at the top of the cabochon is really composed of bands of transparent and opaque material.

The size is 33 mm tall by 32 mm wide by 4.5 mm thick.