The large reddish thundereggs were found at Janos, just south of US-Mexico border and the problem with them is that the large thundereggs tend to contain thin crescent-like agate cores. The miners in the past would break down the large thundereggs to extract the agate cores out so the whole thundereggs are scarce in the old stocks. Recently, a miner finally brought in the whole thundereggs with larger and better agate cores and he has to break the thundereggs in half to check the insides since a low percentage of the thundereggs will contain good and wider agate cores.
   The typical colors are dull yellow to brown and occasionally, the thundereggs are found with brigther red, yellow and black colors. Few thundereggs had been found with brighter colors, tighter banding and stronger shadowing effects.  I prefer to call them "Janos Thundereggs" instead of "Rainbow Agates" to avoid any confusion with the fact that the Brazillian Agates from a specific location and some Japanese agates are passed as "Rainbow Agates". The "Rainbow Agate" may be referred to the crescent-like shape of the agate cores.