The agates of the Sierra del Cachahuen are genetically closely related to those from Malargüe in the province Mendoza. They formed likewise in a sandstone. The agates of Cachahuen show like the agates of Malargüe an irregularly structured, spherical form, which reminds somehow of cauliflower. On the inside these agates show yellowish and red agate formations.Typical for the Sierra del Cachahuen seem netlike structures to be, which are interpreted so far as signs for ruptures caused by drying of the chalcedony during the formation of the agate .