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.
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:
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:
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.
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?