Not much is known about the Coyamo thundereggs since they were on market in the past for a short time. Judging from the pile of cut thundereggs at a rock shop, most thundereggs are geode types lined with thin layer of agate and druzy quartz, and few thundereggs are found with solid white agates. I managed to find one with pinkish hue. The name "Coyamo Thunderegg" is mentioned in Johanna Zenz's "Agates I" book.