The Lithophysae agates (thundereggs) of the Rio Colorado near to San Rafael represent a small sensation, which came since the year 2006 on the market. Their appearance is unusual - in particular if the Lithophysae are not cut as usual perpendicularly against outwardly of the Lithophyse star arm which can be recognized (so a star-shaped picture appears), but parallel to the star arm to be oriented to receive a pattern with a larger agate portion. With this cut, which is rather uncommon otherwise with Thundereggs, then a picture with beautiful eye-like formation can be reached.

Also the variety of colors (of yellow, brown and intensively brick-red tones to a olive-green) as well as the strong coloured contrast, which pieces of good quality are showing, are distinctive for these Thundereggs. It Is typical that the pieces have a opaque character, tranzluzide chalcedony formations are very rare. No pieces with "Uruguay agate Baenderung" could be determined so far. The Lithophysae are reaching sizes up to 18 cm. The agates on the inside usually are showing only few cracks.