A Geologic Riddle

Right. The fossil plant won by a landslide. Batten down your hats, my darlings, because this one is truly bizarre.

I’m going to show you it. But I’m not going to tell you what it is just yet. It’s a bit of a riddle, and I’d like to give you all a chance to figure it out. Ready? Synapses firing, neurons engaged and all that? Then let us begin.

I am black as the moonless night, but I once reached for the light of day.

Mystery fossil I. Note the clean finger for scale.

Touch me, and I am soft enough to leave powdery pieces of myself behind.

Mystery fossil II. Finger endarkened. You can really get your hands dirty collecting this stuff.

Yet I am hard enough to scratch steel.

Mystery fossil III. Note the rust spots on the hammer just above the fossil, and the fact there is no scratch beneath them.
Mystery fossil IV. Preparing the scratch test.
Mystery fossil V. Look at that shiny fresh steel!

What am I?

A Geologic Riddle

20 thoughts on “A Geologic Riddle

  1. 1

    You are: 1) harder than 6 on Moh’s scale, but 2) powdery because of the left-over matrix from which you came and, 3) have the appearance of petrified wood or bone.

    I’m gonna go with petrified wood.

  2. rq

    Carbonized wood fossil. Like really, really old charcoal. Or something. I’m having the gut feeling that carbon is really important here.

  3. 4

    I’m not going to leave a guess, because I read what everyone else put, and my guess was not like theirs and would make me look stupid. Just letting you know a lot of us have no idea!

  4. 5

    Carbonised wood, the shininess on the steel from a layer of graphite rather than a scratch.

    I use graphite pencils to get a metallic effect when making 1/144 models of WWI aircraft.

  5. 8

    Just to clarify, it really *does* gouge into steel quite nicely. It’s very hard stuff, but at the same time, soft enough to rub off on your hands. Dana, did you (I hope) get some photos of the outcrop? I was so tired, I didn’t think to.

  6. 9

    Hmmm. It certainly looks like the picture of jet in Wikipedia, but according to the article jet has a Mohs hardess of only 2.5 to 4. I wouldn’t expect anthracite to be even that hard. Does it burn at all?

    By the way: Thanks to this post I know at least know what jet is! Previously I just knew it was something black.

  7. 13

    1. I can grate grains off a lump of orthoquartzite with a cheese grater. Why do think that the fossil is more firmly stuck together than that?

    2. You are convinced that it is completely mineralized. Why?

  8. 15

    1. With no disrespect intended, I seriously doubt that, unless your cheese grater is made of tungsten carbide or some similar material, and you did specify steel.

    2. No, I do not believe this rock is “completely mineralized,” but it’s nature is such that I *do* believe it would “pretty much shrug off a red hot needle.” That’s not to say it would be absolutely unaffected, but the effect would not be perceivable to unaided senses. I do have a photo, poor quality, different sample, same stuff, taken of a thin section under a microscope. It’s in a publication Dana read during the recent trip, so I’ll have to photograph the photograph, and the quality won’t be great, but at least it’ll convey a sense of how and why I can make some of the assertions I have in this comment thread, with the degree of confidence I suppose it appears that I have. To reiterate, this is a pretty weird material. There *is* a fairly easy experiment I’d like to carry out someday, which I’ll discuss when Dana posts “the answer.”

  9. Rob

    I’ll hedge my bet with two guesses (cheating?)

    I’ve seen something similar at the margins of a marine deposited coal seam where the sample was very high in silt derived from high quartz and feldspar sediments. Essentially a non-combustible, hard, powdery ‘coal’.

    As an alternative, a mineralised fossil high in both silica and manganese oxide (or probably manganese and iron oxides). Possibly associated with geothermal vents (faults or volcanic).

    Entirely prepared to be wrong.

  10. 20

    Is it possible for obsidian to be pulverized enough to form fossils? I remember seeing a lot of it in Oregon, and it looks a lot like that little rock. Wikipedia doesn’t mention obsidian as being a possible ingredient in tuff, but I’ll guess that it’s something like that since no one else seems to have.

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