RTD There is an area north of Willcox, called Deer Creek where an unusual type of silica forms. In fractures between basalt fragments, silica in the form of white chalcedony, brownish chalcedony , white opal and quartz crystals form. The brownish chalcedony can have an odd iridescence, when ground and polished the right way. Then is it referred to as "Fire Agate". This piece may have this play of light. The white opal fluoresces a bright green. The back of the specimen is a sort of geode lined with drusy quartz crystals. Very nice example collected by Dr. Downs in 2009.