Those agates were found in an arid and windy area of Chubut Province, Argentina where the blown sand naturally polished the rough surface of the agate nodules ("Sandblasting") that it can be quite hard to grip them while grinding/polishing them. The typical agate is colorless and banded while some agates have been found with  pink, red, orange and yellow colors sometimes in interesting color combos. El Sombrero Agates are similar to Berwyn Agates but distinguished by their strong red skins.

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Rough Appearance: "Sandblasted" reddish surface by wind, feels very smooth and slippery, can be confused with lighter-skinned
Berwyn Agates from Chubut province. Strong red skins. Pink, yellow, orange and gray colors inside.