The Answer to a Geologic Riddle

You have no idea how impressed I am. I tossed a rather difficult puzzle at you, and within the first few comments, you’d solved it!

Cope was on the right track with a guess of “siliceous petrified wood.” Then RQ nailed it: “Carbonized wood fossil. Like really, really old charcoal. Or something. I’m having the gut feeling that carbon is really important here.” Bam! Three comments in, and y’all had it solved.


This is permineralized charcoal.

Permineralized charcoal. Looks like a little piece o’ burnt wood, and yet you can gouge steel with it.

Carbon is, indeed, really important. So is silica. Lockwood, who studied this stuff in depth and wrote up a paper on it for Oregon State University, sent me the following in an email:

The key here is the term “permineralization,” and more specifically, “silicification.” I think those wikilinks will be clear, but the idea is that all the void spaces, including pores between the cell walls have been completely filled with silica, probably quartz. The reason that the pores are important is that it’s those interconnections that give the rock its overall coherence, toughness, and strength. Otherwise, each individual cell would easily break off from its neighbors. As you’ve seen, they don’t. As a proportion of mass and volume, the carbon is probably only a few percent of the total. So there’s enough exposed on fresh surfaces to smudge your fingers, but the bulk of the rock is crystalline quartz, and is very hard and tough. Incidentally, the carbon *will” eventually get rubbed off, and won’t smudge anymore, until you open up a new fresh surface.

You’re screwed if you wash it, too. I’d scrubbed those samples at work and then tried to demonstrate the trick, only to discover that it no longer performs to specifications. A bit mortifying. You can rub two samples together and achieve the smudge effect again, though, so that’s a little bit of all right. Coworkers were appropriately awed.

The Rose thought it might be fusain, and Lockwood ran with that in the email he sent me:

I don’t think this qualifies as “fusain,” because my read on that suggests that term does not cover permineralized material. On the other hand “permineralized fusain,” while it may be a novel word combination, is probably as accurate as “permineralized charcoal,” which is what I’ve used in the past when I wanted to be as clear and technically accurate as I could be.

We may have just coined a new term, people. Be proud!

Lockwood will be giving us some more detail on this remarkable fossil soon, including a photograph he took of a thin section showing the cells, which are perfectly intact, although a bit squished by compression. This stuff is amazingly detailed: you can see the grain of the wood, and on some samples, you can see the tree rings:

Permineralized charcoal showing growth rings.

At the outcrop, which either Lockwood or I will describe in some detail later, you can see what look like logs of the stuff dotted throughout a sedimentary layer:

Outcrop with permineralized charcoal. Click to embiggen. Note the dark blotches that begin in the lower right, behind the tiny sapling, and follow the light-colored arch to the upper left.

This is one of the reasons I love geology, people. Take a closer look at some ho-hum looking gray rocks with black rocks in them, and suddenly you’re looking at the scene of an ancient forest fire, where logs were turned to charcoal, then silica preserved the remains perfectly. You know how delicate charcoal is. Yet with silicification, it turns in to something that can gouge steel.

Close-up view of the part of the outcrop from whence our samples came.

Lockwood should have a more thorough write-up on this stuff later – I’ll link when he does. He can give us some amazing details, considering he’s the one who studied it in depth for OSU. I’ve got a big-picture sense, a rather blurry one (did I mention this stop came at the end of the day when we were all utterly exhausted?), but he can give us cellular-level detail. And as we delve into the geology of the Quartzville area, we’ll discover why Rob had me applauding with his second guess.

But it’s going to take me some time to pull things together, and I’ve still got to get some research done for our next Prelude to a Catastrophe installment, so we’ll be on with sneak peeks. What’ll it be next? Wild pillow basalts, waterfalls, the weirdest cinder cone ever, or the story of a rather angular erratic?

The Answer to a Geologic Riddle
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17 thoughts on “The Answer to a Geologic Riddle

  1. rq

    Wow, yay us smarty-pants, do we get a prize? Like another riddle or something? :)
    (The reason carbon seemed really important here was also due to the fact that you’re such a huge fan of it, judging from previous posts… and a ‘most bizarre plant fossil’ would most likely get that label from you because it happens to be heavy on the carbon.)
    I would like to add that I am extremely excited about this information, but I’m not sure why. I think it’s because science is fun, and because it all started with a riddle and now I know all about permineralization (ok, not all about, but hey…).

    My next vote goes to waterfalls (because they have such a sparse description in your list and that makes them more intriguing), and second-third tie for cinder cone and basalt.

  2. 2

    I know biologicals are generally grouped (by geologists)into types that do or do not obscure the rocks.
    But has the species of tree, its age and environs been identified?

  3. 3

    hmmm….what I don’t understand is how “fossilized charcoal”, i.e. fusain, differs from “permineralized charcoal”. Wiki says “permineralization is a process of fossilization”. So, if fusain isn’t fossilized by permineralization, by what other process of fossilization could it undergo?

  4. 4

    The best match we could come up with was Trochodendron, but the cellular structure is very- to use the technical term- squarshed, and thus difficult to examine with the detail we’d have liked. Furthermore, neither I nor anyone I was working with had any substantial background in wood identification- we were pretty much working it out on the fly. So treat that guess as a guess, not as anything with some confidence behind it.

  5. 5

    Permineralization is *one* path of many that can lead to fossilization, so it’s a more specific term, while “fossilization” is more general. As an example, the wood at Petrified Forest NP has been fossilized by complete replacement. Little if any of the original cellular structure is preserved in that wood. Molds and casts are other examples of fossils that do not involve permineralization.

  6. 8

    Ah-ha, now I see! Only charcoal that has been fossilized by the process of permineralization could lead to the example, of course. So, could one say that our example is a type of fusain?

    For the record, my knowledge of this is only that which I have been able to google, as I am but a maintenance painter by trade. Having been born in Minnesota, though, I’ve had a life-long fascination with geology — “what? there’s these trippy things called agates that you can just find laying around anywhere?!?!?” Then, later, when I was living in Ayer, Massachusettes, I had an inspirational geology teacher in high-school who told me that Ayer was geologically notable due to the fact that it contained every land feature that could be produced due to glacial forces?!?!
    So, I just wanted to say thank you so much for the free lesson in permineralization — I really appreciate it! Thank you, thank you, thank you — Love your blog too, Dana. Thank you.

  7. 9

    First, no one is “merely” anything. Second, geology is a blast at many levels, and it’s a shame the US educational system treats it as a throw-away discipline. Third, one of the many aspects of geo I love is sharing it, so my pleasure. Finally, to the topic at hand, my sense from the wikilink is that fusain properly is simply charcoal- unmineralized- in the geological record. And technically, even unmineralized, that would be a fossil. This is simply a “variety” of fusain, or charcoal, that *has* been permineralized.

  8. 10

    Wow, I see!


    Thanks for going over the distinctions with me. Now I have a much better understanding of just what fossilization does and does not neccessarily mean.
    You’ve been very generous with your time and sharing of knowledge, and I really appreciate that.

    Thanks, again.

  9. 11

    BTW, the experiment I mentioned yesterday I’d like to try is to take a an acetylene torch to bit of this- hot enough to see if the carbon would burn out. Alternatively, put it in a good, hot kiln for a while. I’m sort of curious to see what it would look like without all the carbon in it, and in fact if you can, with exposure to prolonged high temperatures, burn the carbon out. As I said yesterday, it doesn’t burn, and I haven’t even been able to get the aphalty, coaly smell I was kind of expecting.

  10. 12

    First, no one is “merely” anything. Second, geology is a blast at many levels, and it’s a shame the US educational system treats it as a throw-away discipline.

    Can I get an AMEN?!

    Lockwood is preachin’ to the choir in my case. I teach Earth Science to 8th graders. In my school district, this is their last (really their only) shot at Earth science. As a result, I attempt to teach as many of the high school content expectations as possible – to middle schoolers.

    I live in a different district, where my daughter was told that she was too good a student to take geology when she was in high school.

    In fact, I was a biology major, and had never even taken a class in Earth science when I was assigned to teach it. I fell in love with it, and haven’t looked back. The fact that I had no background in the topic gives you some indication of the esteem in which it was held, but wait – the teacher I replaced was a music major. To be fair, I’m sure he did better job teaching Earth science than I would do teaching music.

    I’ve worked hard to raise awareness about the importance of the Earth sciences locally, as well as at the state level. I like to think that I have made at least some small difference.

  11. 13

    It really is sad… geology is treated as the science that “people too slow to get science” get shunted into. As if it’s all easy to get, and as if other sciences can’t be introduced at more appropriate levels for less advanced students. This outcrop and many, many others, are puzzles that took me many visits over many years to come to tentative answers that I’m comfortable with- but by no means feel like I’ve “solved.” ‘Tain’t easy, McGee. At a more basic level, I think our lack of geoliteracy is a major reason we build and crowd into at-risk areas, however desirable they may look, making mass death almost unavoidable. Then when the worst happens, we are told “No one could have anticipated.” “Yeah? I could’ve. But you’d never think a geocientist was worth talking to until after the fact. And you pointedly ignored the ones who *did* anticipate it, and tried to sound the alarm, until it was too late.”

  12. F

    Well this has been fascinating. Do we have any idea when the stratum this was found in was formed and and under what conditions? I wouldn’t know where to begin searching for information on this. I’m not even certain you specifically identified where this was in your travels.

    Whatever, if someone can point in a general direction for me, I’ll dig. Is all this stuff in the Willamette Valley?

  13. rq

    My older brother is a geophysicist (so lots of geology) and the things he talks about don’t leave me with the impression that someone who ‘doesn’t get’ science should be doing it… But anyone can ‘get’ science, if it’s introduced in the right way (here I’m VERY grateful to a couple of high school teachers who were excellent presenters of basic material and made it simple and fun). Also, if people didn’t have the general idea that science has to be difficult – which seems to be a universal constant – they would be a lot more prepared to listen and to absorb and to realize that it isn’t all math equations or complicated naming systems, and actually very practically doable stuff that is FUN.
    I just talk about how much fun I have in the lab, and people look at me like I’m nuts, which I find strange, because they’ve never tried it and it confuses them… I’m not sure how else to change that ‘science is hard’ attitude, but there must be a way to change people’s minds en masse.

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