My Favorite Things: Thundereggs

by Emerian Rich

Name: David Rix

Current obsession: Thundereggs

There is something to be said for specialisation.  When you are a collector and driven to look closely at the world, keeping things specific is a defensive measure against the sheer scope of what’s out there.  I guess that’s why, of all the unending world of rocks, minerals and crystals, I collect thundreggs …

picture 1 a few American thundereggsThundereggs – some of the most extraordinary and beautiful natural formations this planet has ever produced.

How these things actually form is still not known for certain.  It can be stated that they are formed in a certain specific type of lava flow that gives rise to a certain specific type of rock (rhyolite) that sometimes contains a certain specific type of nodule.  An often dull round nodule that gives little idea from without what wonders it can contain.  Beyond that, it is more speculative but during formation, the nodule splits and tears open, probably as it cools and contracts, forming a hollow centre.  And it is this sense of torn stone that defines a thunderegg in aesthetic terms.  Thundereggs have a stress and energy about them that is unique – you can sense the earth’s intense heat and violence in their past – rock that flows and swirls, filled with life, before it was frozen.

But that is only the start.  That is the fiery birth.  It is what happens next that makes them so special – as the little hollows within these stones are filled with further growth of glittering crystals and colourful banded agate, and maybe other things like mineral moss.  How it happens is still the subject of much arguing, but it seems most likely that the interiors, or ‘cores’, are built up over an extended period, and sometimes in many phases. Thundereggs thus contain a kind of geological narrative as layer after layer builds up, sometimes of different materials and structures.  Following the ‘narrative’ of a thunderegg can be one of the most enthralling aspects of these stones, especially when something occurs to disrupt the process – when you can see traces of events that must have occurred in the far past.  The age of these rocks ranges from about 30 million years to over a billion years – that’s all the way back to the time of the simplest life.  That is a long time for a rock to sit there in the ground.  Continents move, supercontinents form and break, rock layers shift, earthquakes strike – and these also become part of the narrative.  If the ground moves while the core is still forming, the patterns will change with the changed alignment, producing tilt eggs, as can be seen in picture 2.  But even after the formation is over the narrative continues, as geological stresses continue to assault and change the stone, creating flaws or even shattering it completely before reconsolidation.

picture 2 a few narrative thundereggsThe crucial thing, the thing that makes thundereggs so collectible to a degree that is extreme even for rockhounding, is that the appearance of the rock and what happens inside is unique to the area it is formed in.  As well as the story that has followed it over the years, every thunderegg carries within it a stamp of the ground and world in which it sits.  The results are dizzying – like wine taking on unique characteristics from the soil, but many many times more so.  Thundereggs from different continents can be so different as to be almost unrecognisable.  Different volcanic areas likewise.  Different individual flows of rhyolite lava … different layers within the flow … different deposits of thundereggs within the same layer … different sides of the one little pit you just dug in the ground … and this is why once you start collecting these things, there is almost no escape.  Especially if you have a cataloguing mind, like I do.  For people who know these stones, it’s never just a “thunderegg.  It’s never just a question of saying “this is from America”, or “this is from Oregon” – sometimes not even “this is from Mount X in Oregon.”  It could be “Mount X, bed three, lower level, 2014 diggings.”  And then of course there is the endless variation of pattern and material that, to all intents and purposes, goes on forever!

picture 3 a few German and French thundereggsI have been working with these things for years now – I have even discovered a few of my own, I believe the first specimens known to the scene from the UK.  I learned to polish them, which is a long and messy job but infinitely rewarding.  I learned to cut them as well, which is if anything even more magical.  Imagine taking a simple lump of rock and slicing it in half with a diamond blade.  There comes that moment when the rock falls into two pieces and you get that first look at what’s inside, in all its endless possibility.  You rinse the mud off and hold it up to the light to see something that no human being has ever looked at before.  There is a magic in that.  And you cut more – and more.  Until your garden is filled with piles of rough rocks and scraps – until you have paid enough having them posted round the world to finance a small house.  You fantasise about beating customs officials with a big stick.  You wonder why you can only get specimens out of Russia with an ornamental clock attached.  You tear you hair at reports of thundereggs from Antarctica or from the bottom of deep lakes that you will never get your hands on.  You wonder if there are any thundereggs in North Korea and mutter about global politics.  You start to ask questions about Martian Blueberries.  But you go through it all anyway – you have to.  Passions are unconquerable.  Once thundereggs become a part of your life, the chances are that they will remain  so, even though they are a journey you know you will never finish.  Like most journeys, when you get right down to it.



David Rix is an author and publisher. He runs and creates the art for Eibonvale Press, which focuses on innovative and unusual new writing in the areas of Slipstream, Speculative Fiction and Horror.  His own published books are What the Giants were Saying and the novella/story collection Feather, which was shortlisted for the Edge Hill prize.  In addition, his shorter works have appeared in various places, the most notable being many of the Strange Tales series of anthologies from Tartarus Press, Monster Book For Girls from Exaggerated Press, and Creeping Crawlers from Shadow Publishing.  As an editor, his first anthology, Rustblind and Silverbright, a collection of Slipstream stories connected to the railways, was shortlisted for the British Fantasy Award in the Best Anthology category.   He is currently at work on his first novel, A Blast of Hunters, and several novellas. 

Having spent much of his life by the sea, which has left a permanent influence and deeply infused Feather, he now lives in north-east London.  The city life has led to both an increasing urban feel in his writing and to the hobby of cycling round the city at 3AM with his camera, photographing the infinity of this bizarre place. Find out more at:

Author homepage:

Eibonvale Press:


Thunderegg Gallery:

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