I have heard that called several different names, Tennessee River chert, Buffalo River chert, and a bunch more. It is part of the Ft Payne formation, it is a type of jasper. The yellow does not normally change color but if it does, it turns a deep burgundy red. Usually, the yellow is called Tennessee River chert and the red, blue and purple are called Buffalo River. It is the same rock, it just comes from different areas. Bill