… Or, As Rockhounds Say It … “Thundereggs”
(See Note at the end)
The name always sounded to me like it was a slogan made up by some ad agency: “Eggs From Thunder!!!”
But there is a genuine history behind the name. The Warm Springs Indian tribe, on the eastern side of the volcano cluttered Cascade Mountains, thought that the Oregon thundereggs were thrown by the thunder-gods from the high, snow-capped peaks. In fact, that has been a popular theory with a lot of people. It probably still is for some. The truth is more complicated and more interesting.
Most people associate thundereggs with the abundant deposits in central Oregon. It’s the state rock in Oregon. The little town of Nyssa, Oregon even has an annual festival to celebrate them. (I think … Their Facebook page hasn’t been undated in six years.)
Oregon thundereggs were first found at Priday Ranch, north of Madras, Oregon. Today, Priday Ranch is a conservation area. The famous thunderegg beds are now called Richardson Ranch. You can’t dig them yourself anymore. You can’t even pay to dig there. You can buy them in the gift shop. (Sigh!!!) Rockhunting isn’t like it was when I was a kid with my dad on the desert.
I have to share a plug for the most comprehensive thunderegg website I found while researching for this blog. “Markus” is apparently an individual who created the page but he’s doing an amazing job. And there are pictures! Check it out at: https://thundereggs.jimdofree.com/ .
I also have to praise an amazing book about thundereggs. “The Formation of Thundereggs” by Robert Paul Colburn. A lot of the information I quote here is from Colburn’s book and he quotes sources so you can verify it. The “Kid” at the top is Colburn.
I learned at the comment page at Markcus’ website that Colburn, ‘the Geode Kid’, has passed now. But you can still get the book from the original publisher. (And a bunch of other cool books too!) The details are at: http://donaldkasper.com/index.html
You can get more details about Colburn's book at:
For an “amateur” geologist, Colburn’s book includes more technical details about the geological processes that result in a thunderegg than most people will want to read. But he also includes some practical gems. When discussing what you might find at Rockhound State Park, New Mexico, he offers this gem:
“… the good eggs are surrounded by the yellowish-tan clay, while the duds are within only unaltered black, glassy perlite that allows the experienced digger to determine and throw away the duds and take only the good.”
I absolutely love the way Colburn destroys “academic” geologists who apparently ignored evidence scoured from the Earth by humble rockhounds. In a formal, peer-reviewed scientific paper, three authors from prestigious institutions state, “Examples of spherulites larger than a few centimeters are rare …”. Colburn includes a photograph of three that he found that are clearly bigger than a few centimeters. (The three in the picture at the top.) It’s far from the only example in the book. The next hundred pages are filled with similar examples.
I’ve experienced the same thing from people with advanced degrees. Colburn writes, “If I could only find someone who would, on basis of fact, determine that the observations and data I will present are flawed, I would still consider this work a success.”
A-men, brother.
Although Oregon gets most of the attention for thundereggs, they’re actually a type of rock found in various places around the world. Markus has compiled a very long list of locations at his website. But the message page has additions that Markus missed anyway. I still have some of the “red agate” thundereggs pictured here that my dad found somewhere in Utah. I don’t think these are represented in the list published by Markus.
Thundereggs do have a unique story about how they’re formed. Thundereggs are not just agate nodules. For example, nodules like Brazil agates or Laguna agate don’t have the internal “star” structure of thundereggs. What’s the difference?
One thing to keep in mind as you ponder the question is that geologists are still arguing about it. As an example, one theory is that “hot gel” was responsible for the formation for thundereggs. The idea is that silica gel (think of it as hot, volcanic agate) fills a cavity directly out of molten rock which then spontaneously solidifies into today’s thundereggs. That idea comes with buckets of problems, however. An example of a problem is the inclusions frequently found in thundereggs, like calcite crystals, manganese dendrites, and sagenite plumes. These are completely incompatible with “hot gel”.
The key to understanding the formation of thundereggs is to realize that the thunderegg shell (for example, the brown outer material in Oregon thundereggs) and the cavity (the “agate” interior) develop in totally different ways. A second key to keep in mind for this blog is that it’s a vastly oversimplified version of something Colburn explains in 497 pages.
There is a grundle of geological action that takes place between baby Earth and it’s molten surface, and rhyolite, the cradle of thundereggs. Think of rhyolite as silica-rich lava that cools fast on or near the surface rather than deep underground. It’s also the key to the formation of jaspers like wonderstone. You can read pages and pages about it in Colburn’s book.
Colburn’s theory, based on his work with hundreds of thunderegg deposits and scientific papers, is to start with cavities created by gas bubbles in lava that become filled with water-based minerals, principally our old friend, silica. This is also the way non-thunderegg nodules, like Brazil agate, start out.
According to Colburn, thundereggs only form in rhyolite lava domes and flows and not in ash-flow tuffs or welded ash. This provides the environment that allows the spherulites (thundereggs and their earlier gas bubble forms) to migrate gradually to lower pressure depths and release volatiles such as CO2, SO2, and especially water locked in pores and crystal lattices of the rhyolite through the corner vents in the outer shell that are so clearly present. Other minerals enter the spherulites the same way. And the final action is for the silica to form over millions of years in the cavity left behind.
Colburn shows the stages of development and depth in thundereggs that became geodes from a deposit he personally mined. Keep in mind that every deposit of thundereggs is a unique creation of nature and the processes that created it are similarly unique.
Stages in the development of thundereggs from a mine near Contact, Nevada – from Colburn’s book
Colburn also maps the layers in the Priday Ranch thunderegg deposits that illustrate the same thing. The changes in the thundereggs found at the different depths approximate the changes seen in the Nevada mine.
I have to warn you again. If you want the real, detailed story, you’ll have to read Colburn’s book.
But now, it’s time to lay down my rockhammer and pick up my philosopher’s pen. Why do geologists (and other scientists) get it wrong? The first answer is, “They don’t. They get it right far more often than they get it wrong. And even when they do get it wrong, the scientific method is self-correcting. They clean up their own messes.” But they do sometimes get it grossly wrong.
One of the best examples is continental drift, which was proposed by Alfred Wegener in 1912. The biggest problem with his idea was that he was a meteorologist, not a geologist. (Wegener died in pursuit of his own science in an arctic expedition.) It took over fifty years for the geologists to wrap their minds around his idea -- mainly because they were forced into it by overwhelming evidence.
The creation of the Washington scablands east of the Cascades is another example. J Harlen Bretz told the establishment geologists that they were formed by cataclysmic floods in the 1920's but that idea was completely rejected. When he was finally proven right, "Bretz received the Penrose Medal, the Geological Society of America's highest award, in 1979, at the age of 96. After this award, he told his son: 'All my enemies are dead, so I have no one to gloat over.' "
I see this as a problem with people, not science. There are cycles in human behavior that seem to get repeated again and again. Plato was a student of Socrates. Markus seems to be a student of Colburn in a similar way. Socrates was forced to drink poison by the “establishment” in Athens for expressing ideas too new and different. Wegener was ridiculed back into his purely meteorological studies and disappeared into the arctic. And Aristotle’s ideas were frozen into dogma so completely that it took more than a millenium (and the lives of many free thinkers) to thaw the process of discovery enough for anything new to even be allowed.
Science is like what Winston Churchill said about democracy. It’s a terrible way to try to discover new truths. It’s just much better than whatever is in second place.
--- Note ---
Note – Lithophysae: “A lithophysa is a felsic volcanic rock with a spherulitic structure and interior cavity with concentric chambers. Its outer shape is spherical or lenticular.” (Wikipedia – Now … Aren’t you glad you asked!)
Comments