Fire agate is only found in southern Arizona and northern Mexico. The rock on the bottom is what it looks like originally. It has to be cut by hand as the color is only a few microns thick (which is why you rarely see them in jewelry stores, and when you do they're fairly expensive). It is similar to Australian opal in that it formed with water and has chatoyancy (shimmering colors).
Please view in high res to see the stone's color better, if you have time. (5 years and 2471 days ago)