This is a stone where we have just chipped or rubbed  to expose the natural fire agate pattern under the Chalcedony layer.
will be fun to cut and polish.
or leave as specimen
as per images

 This stone was mined in Mexico but it is found in Arizona also.The stone appears to glow inside like opal.The gem is thought to be formed when hot water saturated with silica and lava oxide invade cavities in the rock and cool. Chalcedony with iron oxide begin to grow on the surface.The iron oxide gives the basic brown colour to the stone.It grows layers of silica and iron oxide. These alternating silica and iron oxide cause the brilliant fire from the stone.After the iron oxide ran out of the specimen colourless chalcedony contained to grow over it.