Agate cast after Fossil Coral (rare) Kay Robertson Coll.

Item Description

Fantastically unusual looking and rare agate from an unknown locality in Sonora, Mexico. Agate has replaced (casted) a striking spherical cluster of intergrown coral heads. You can see radial coral growth of the elongated colonial corals on each of the flower petal-like coral heads. Ex Kay Robertson Collection # 1380 and acquired in the Spring of 1962. An alternative possibility on Kay's label is that this is the highly unusual center of a thunder egg - a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. Thundereggs are rough spheres (Wikipedia). Kay is a prominent California collector, who specialized in European classics (see the article in the March-April, 2007 Mineralogical Record).