How to Determine Proper Orientation for Successful Cutting of Lithophysae:
Most nodules and geodes of any species have features on their surfaces that an experienced lapidary artisan can identify by sight for cutting so as to capture all of the best features within. For example, many thundereggs (lithophysae) have lines known as flow bands on their exteriors and, unless a deposit has been deformed prior to filling, a cut made perpendicular to the flow banding and through the long axis (for the widest face) will yield a cut face showing the sequences of agate, waterline "floors," and stalactite deposition "right side up." If a formation has been tilted by a diastrophic event, subsequent filling will be at odds with both the flow bands and the long axis-- which can make orientation difficult, but not impossible.
Biconoid thundereggs-- eggs with a biconic core present a special problem. Most of these eggs will yield a face with a high degree of matrix if not cut properly. However, the pressure ridges left behind when a spherulite degases into a lithophysa are the key. Cut along the pressure ridge in a biconoid to achieve a larger agate face. Pressure ridges are a key to cutting orientation in any egg in which they are found on its surface.
Many collectors speak of "lucky cuts." There are no such thing-- only a lack of knowledge about the structure of lithophysae.
In any case, a fool proof method can be used to determine a proper orientation for any eggs dug directly from the material in which they form: While digging, when you "hit" one, carefully uncover enough of it to see the top and front, without removing it from in situ. Mark the top and draw a line towards you or a compass point with a broad black felt-tip marker. Record the compass point and mark every nodule the same way. After cutting just a few, an angle departing from that mark will be found which will expose the most interesting features, and with care, the value and beauty of your nodules will be increased.
More detailed information can be found in my forthcoming book, The Formation of Thundereggs.
Home-page of the Basin Range Volcanics Geolapidary Museum
What Are Thundereggs(Lithophysae)?
Where To Find Thundereggs (Lithophysae)
The Collection of the Geode Kid
Baker Thunderegg Basics
Where To Find the Basin Range Volcanics Geolapidary Museum and Rockshop
You can e-mail us at
You can snail-mail us at
Basin Range Volcanics Geolapidary Museum
6235 Stirrup Rd SE
Deming, New Mexico 88030
For more information,
please refer to my book, The Formation of Thundereggs
by Robert Colburn, aka "Paul, the Geode Kid."
This web page was created for the Geode Kid by Carlton J Donaghe and Bill Boomhower
All contents copyright © 1997 Robert Colburn. All rights reserved.