Sunday, October 31, 2010

Accretionary Wedge #28: Halloweeny DeskCrops

Trick or Treat

It's time for another Accretionary Wedge. This month's theme is "Deskcrops," which I had intended to use as a showcase for the weird and wacky stuff that we geologists accumulate over the years. I've seen departmental collections where the strangest things were in there. "Pebbles and Mortar" from Hadrian's Wall; flesh, bone, and adiposere (fat) from a dead rhino; 1 mL of Deuterium (heavy water); and many more strange and beautiful things.

Seeing that it's Halloween (and also my Birthday), I thought it might be neat to go Trick-Or-Treating in the geobloggers to see what I get. When I was a kid, I would split my loot into different piles. From stuff I liked, to things, like "Bit-O-Honey" that weren't really very good. Fortunately for me, all the stuff I got was great - and roughly fits into categories related to the rock cycle.

This was my costume:

I'm going to give pride of place to my contribution: a few chunks of Trinitite: the glass made out of fused sand and rock and bits of equipment (casing, wire, etc) that formed in the explosion from the first atomic bomb.

It doesn't look like much - just some greenish, glassy stuff - several vesicles, and "blobs" of melted, spherical droplets. It has a little radioactivity above background. But I did notice some interesting bits. It does have parts that fluoresce in long and short-wave UV light:

There are a few flecks of orangy things. The chunk of rock they're sitting on is also showing off some nice fluorescence. I blogged about this chunk last week.

It's under short-wave UV that the Trinitite really shines (pun intended):

I don't know what's causing the red, orange, yellow, and white colors. It's probably a fascinating melange of stuff incorporated into, altered, or formed during the explosion.

So, let's see what else I got...

Igneous Rocks

First off, we'll go with igneous rocks. These are rocks formed by the "freezing" of molten rock. These rocks may form deep below the surface as an "intrusive," or erupted onto the surface as an "extrusive" rock (often in a dramatic volcanic eruption).

Philip at Geology Blues provided some "Lavasicles." And tells a tale of finding neat rocks hiding within an existing collection. No need to traipse around the world, just capitalize on what's at hand. Kind of like MacGyver...

Jess at Magma Cum Laude (she's probably still unpacking at her new blog-home) tricks us with an interesting scorch pattern on some pumice from the Sufriere Hills.

Garry, the Geotripper, shows off some lovely peridotite xenoliths. And provides a keen quote to boot!

Ian from Hypo-theses, continues to blog about a rock each day. Quite a challenge. You know the post is going to be interesting when the exposition begins with a story about sitting around a bedouin campfire on the edge of the Sahara. We're treated to many photos of some kind of long-named, Norwegian pegmatite. Check out those phenocrysts!

Lockwood's blog, Outside the Interzone, gave us a neat hunk of pillow basalt. It includes the classic field photo (hammer for scale) to show its provenance. Also, not the only blog to photograph the rock with a cat for scale - there might be a theme here...

Sedimentary Rocks

Sedimentary rocks are either "clastic," which are made of broken fragments of pre-existing material compacted, cemented, and turned to stone. Or, they are "non-clastic" - I've never been a fan of classifying something by what it's not - so I prefer the term "chemical" for the other group of sedimentary rocks that are formed by precipitation out of solution.

Anne, over at Highly Allocthonous shows off some nifty cubes of rock she uses to teach about porosity and permeability. Incidentally, my house lies about 20 feet above the Eau Claire Formation in the stratigraphic sense. There's a slice of the Wonewoc and some unlithified sand/gravel outwash between us, but some of my drinking water comes from this aquifer. Many of our local springs form as a result of the interbedded shales that form local aquicludes (even perched water tables in the hills nearby).

Silver Fox, who is still Looking for Detachment, shows off a very Halloween-y hunk of dolomite breccia that looks like a Jack-O-Lantern. These kinds of rocks show that the distinction of "clastic" or "chemical" are not always useful. The big pieces of gray dolomite are clasts, but the whole thing is made of and cemented by the precipitation of minerals from solution.

Having been properly tricked, David at History of Geology provenance, shows off some lovely fossils from the eponymous "Dolomites." Incidentally, carbonate rocks are relatively susceptible to chemical weathering, but often resistant to physical weathering - especially in arid regions where they slowly weather into sharp little points and edges, that give rise to the term "tear-pants" topography. Those of you who have sat on these rocks have probably noticed how quickly this texture can slice open clothing, boots, and hands.

Metamorphic Rocks

A metamorphic rock is what happens to rock subjected to increased heat and/or pressures. These produce new textures and minerals as the rock deforms in response to these changes.

The Musings of a Life-long Scholar shows off a "deskcrop" that doesn't take up much space - a backscatter electron image of a monzonite grain. Photographs often contain a lot of data, and they take up much less space than the actual material.

Dana Hunter over at En Tequila Es Verdad, provides a few images. The first is a Schist, followed by a meteorite, and then the "peacock" ore, bornite. Also with cat-for-scale photograph.


Then there were some treats that didn't fit into a nice category. Like the multi-treat packs, they had a little bit of everything, or their post had some other geologically related theme.

Callan Bently and his Mountain Beltway, also unpacking into a shiny new home, shows off a bunch of samples. Does a vodcast count for a blog carnival? Seems kind of "fancy" for this show since everything else looks monodimensional by comparison. Kind of like being the following act after the talking pig at the county fair.

Helena Heliotrope from Liberty, Equality, and Geology shows off a spikey dogtooth spar and a hunk of orpiment. Orpiment is a pretty (if toxic) mineral with a chemical formula that's easy to remember As2S3. Just omit the subscripts. This works even better for Realgar.

Julia over at Stages of Succession shows off some "Labcrops" of biological specimens, including multicolored mammalian crania, critters in jars, and a few colorful remarks. I'm rather partial to the red maxillae and yellow frontals on the skulls.

John - from Karmasotra - shows off some clamshells. I believe they're all Mercenaria sp., showing various growth and bioerosion development stages. Plus a creepy comment about preserving beauty through death. What was that quote about "leaving a beautiful corpse..."?

Finally, one more trick: Ron Schott's Geology Home Companion, blogfather to many, and inspriation for this theme said he was working on a post. I'll link to it when it appears.

The "tricked" blogs are all there, you just have to figure out how to see them... (hint: try selecting text).

I think I've gotten everyone - please alert me to any errors or omissions.

UPDATE: Ann,who muses on geology and other things, has a post. It got lost in the shuffle and I wasn't able to find a link to the post until today. She writes a few musings about a piece of amber. As you may know, amber is the fossilized sap of trees. It has the interesting property of being slightly less dense than salt water, so sometimes chunks of amber erode out of the rock where they are preserved and wash up somewhere down the shore.

UPDATE 2: Jazzinator (aka Dino Jim) has a post to add. It includes a nice spooky story of a scary mineral. No trick, I guess. I figure being at the bottom of the post is tricksy enough...


  1. Entertaining posts this month! Thank you for hosting!

  2. Very nice! I read this first on mobile, and there weren't any "tricks," so was confused at first when I clicked through. "Select All" worked for me. :)

  3. Thank you Matt, I can't tell you how much I really appreciate it to be finally included. I also like the comment you made. I've been doing accounting books for so long I sometimes forget these details. The interesting thing with that piece is you can see some holes where it looks like something tried to burrow into it on the backside, and it has been rounded by the water. Also there appears to be some small salt crystals in the holes too. I tried to take a picture of it but my camera just couldn't capture it and do it justice. Also do you thing that texture could have been cause by shrinking, like mud cracks since they are polygonal in appearance (the problem I've had with that is they do not radiate inwards, but I am dealing with weathering too) are you aware of any other examples of shrinkage cracks in amber? Or do you think it might have come from being next to an animal skin? It is a fun piece to pick up and ponder upon.
    Again thank you, I appreciate you input for not knowing why it hasn't been updated.
    Ann Willis

  4. Sorry for a little late but here is my addition:

    Great idea and awesome post

  5. the glowing of your stones from trinity... is radiation dude, you didnt know that?

    radiation takes thousands of years to dissapitate. what you are seeing is residual radiation, not some form of mineral...

  6. Hi Hop1pop,
    When you refer to "glowing," I assume you are referring to the orangey color that you can see in the piece of trinitite (which is really just a fancy name for fused silica glass formed as a result of the trinity atomic bomb test).

    Well you are correct in that it is some kind of "radiation." But you are using the term radiation in a very general sense, while I am being much more specific. I think this will take a blog post, and not just a blog comment to really flesh out. But let me hit a couple points you raise in your note:

    1) The "glow" is not ionizing radiation, which I assume you are implying with your statement. There is some residual ionizing radiation that can be measured with a geiger counter, but it is not much. The glow visible in the sample is called "fluorescence." This is a type of "radiation," but it is radiation that is occurring as visible light (which is produced as a result of stimulation by higher energy photons).

    2) This idea that radiation takes thousands of years to dissipate is not wholly incorrect, but it is far too general and non-specific to be helpful in this case. Some sources of ionizing radiation takes many thousands of years to decay, while some sources may last for billions of years. Other sources may decay in mere days or even milliseconds. Notice I said "decay" and not "dissipate." Dissipate implies that there is the same amount of something, but it is scattered, or dispersed. A source of ionizing radiation, however, is not simply dispersing. The atoms in that source are - for purposes of shortening my comment - breaking apart. They are decaying into something else. So as the source decays, it emits radiation and the amount of that source decreases with time (which, as I previously mentioned, may be of long or short duration). It does not necessarily "dissipate."

    So there you go - that's what you get when you try to be glib with a college professor. You get much more than you bargained for. Plus, I've got a great idea for another sequential illustration discussing this idea of "glowing radiation."

    Thanks for your input, I hope you've learned something about radioactivity that might be helpful in the future.

  7. I had intended to carve an actual watermelon into the shape of a tourmaline crystal thus making a literal "watermelon tourmaline", but I never got it done. Sorry.

  8. Oops. The watermelon tourmaline was what I had intended to do for the 2011 Halloween themed Accretionary Wedge. Can't even remember now what I had intended for this one.


  9. A watermelon tourmaline would have been awesome! There's always next year :)