The THUNDEREGG...
Born in a rhyolite matrix (acidic lava), thundereggs (or lithophysae) are created from a "hollow" in the volcanic matrix. Its filling, sometimes with agate, sometimes with jasper, remains silica-based.
The thunderegg offers a huge span of colors and patterns, and it's quite easy to recognie its occurence and location.
At Pareidolia-Unica, many thundereggs are presented: these from US (Richardson, Buchanan...) or China (Liangshan, Pujinag...), those from here (La Vigne, Darboussières, even la Tour de Mar or Le Forestier..), and many more.
See these round to ovale shapes and their colored core!
Detail: Lava Cap thunderegg, New Mexico, USA.
