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The River Rio Uruguay is forming the frontier between three southamerican staates: Uruguay, Brazil and Argentina. In some gravel pits at the argentinian banks of the Rio Uruguay river, long distance transported alluvial agates can be found. Some agates ar not only edge-smoothened - they even look as they were being polished by the fine sediments in the river. The most beautiful agate nodules are reaching a size of 12 cm in diameter. Their pattern is showing more evidences for the long transportation: secondary colorization by iron-pigments and bleaching by humidous acid.

Besides fine banded agates a lot of different jasper-like formations (similar to conglomerates, pointed varieties and many more), mossy-like- and plume-agates and petrified wood can be found here too.

In the USA rough nodules from this locality are offered as “Black River agates” from Patagonia. Collectors are keeping those specimen in their natural shape and do not polish them (20, 21, 22).