Complex Buchanan Thunderegg Geode

7.5cm

Now this is a really magnificent specimin - and quite an unusual one in several ways. Firstly it is from one of the 'other', less usual buchanan beds characterized by a darker coloured matrix (that's all the info the seller had) - and secondly - well, just look at that cave! What on earth is going on in there? Is this one of those formations left behind after crystals have weathered away? Or some other form of mineralization? I really don't know. At any rate - the colour scheme here is amazing, thanks to the darker matrix.