The Cerro Negro Mountain represents one of the many find zones near to San Rafael. The nodules which come from here, were picked up a long time only from the surface. After these findings became more meager, also one tried to find by excavations agates. Typically for agates from  the Cerro Negro Mountain is a irregular surface of the nodules which is greenish in many cases. Often agates of the Cerro Negro are colored in bright colors. Usually the colored banding begins after a colorless to weakly teinted external area.