Rocks for Danarra

Note: This is cross-posted at my geology blog Georneys.

I am a terrible person sometimes. In particular, I sometimes procrastinate actions that really don’t take much time but which I cannot, for whatever reason, handle at a particular time. I think I feel most guilty about being a library book thief. I often procrastinate returning library books. I stole at least two books from my high school– they are still on my shelf at home. I will return them at my next reunion, along with a donation to the library. In college I paid about $200 in late book fees before I was allowed to graduate. Here at MIT I have probably only paid about $100 in late book fees, but mostly because I can renew the books so many times. I love the library policy at Woods Hole Oceanographic Institution- you can check out books for a whole year, and if they’re recalled or you’re late returning them the worst that happens is that the librarian harasses you by email or- in one case where I was in the field- confiscates the late book from your office shelf. If I am ever very wealthy, I will donate generously to all the libraries I have abused over the years… after buying the town of Al-Wuqbah in Oman sparkling new bathroom facilities, but that is a story for another day.

I suppose there are worse things in the world than being a library book thief. But I also sometimes procrastinate other things or cancel commitments when they are just too much. I can’t explain it- I hope that when I’m not so busy and stressed with graduate school that I will be better about certain things, such as returning library books. When I am really busy and stressed with school, I don’t even make time for rare social events, such as my weekly trip to the rock gym or hanging out with friends. I guess when I’m stressed about my PhD I can’t handle any other commitments, even when they’re small (like returning library books) or fun (watching a movie with friends). Some days/weeks/months I do better than others. But many a Friday night I sit at home watching TV with my cats, relaxing from a stressful week before heading back into lab on Saturday.

I used to procrastinate blogging on Skepchick when I was stressed with graduate school… now that I have my own blog which I am making an effort to post regularly on (in addition to occasional Skepchick posts), I am going to try to un-procrastinate at least a few items. First on the list? Mailing some rocks that I should have mailed back in July.

After a long absence from Skepchick blogging, I posted a Where in the World is Evelyn the Geologist Quiz. Loyal Skepchick reader Danarra won this quiz, and I was supposed to mail Danarra a rock. A month later I apologized and promised to send two rocks. Then I had a stressful committee meeting and a trip to Africa and such… and I never sent the rocks.

About four months has passed since I was supposed to sent Danarra a rock. So, to make up for it, I am sending four rocks… one for each month of procrastination. Below are pictures and descriptions of the rocks, and they will be off in the mail first thing tomorrow morning. I apologize, Danarra, that you were the victim of one of my procrastinations. I hope you enjoy your rocks!

Four little rocks (with descriptions) for Danarra.

Rock #1: Obsidian
This rock came from a stash of rocks I collected on undergraduate geology field trips. In the old days (er- does five years ago count as the old days?), I didn’t document my rock collection as thoroughly as I do today. However, the bag this rock was in was labeled “California Trip” and I’m 99% sure that I picked up this piece of obsidian at Obsidian Dome in California.

What is obsidian? Obsidian is volcanic glass. Obsidian forms when felsic (high SiO2 content and very viscous) lava cools extremely quickly. Obsidian was commonly used in ancient times to make points and blades for tools and weapons.

Rock #1: Obsidian.

Rock #2: Garnet-Mica Schist
This rock came from an even older stash of rocks that I collected in high school and before. This rock likely came from my native New Hampshire, probably from my parents’ dirt driveway, which is littered with these garnet-rich mica schists.

What is a garnet-mica schist? Well, let’s break down the name. A schist is a medium-grade metamorphic rock. A metamorphic rock (for you non-geologists) is basically another type of rock which has been squished and heated but which has not completely melted (that’s an igneous rock). However, the rock has been changed in some way by the squishing and heating. In this case, the rock probably started out as a clay and/or mud rock. When this rock was squished/heated, new metamorphic minerals formed: mica (too small to see with the naked eye, but they make the surface of the rock shiny) and garnet (the little red-orange bumps).

As a quick aside, geologist are very fond of saying to each other things such as, “Wow, that’s some great schist!” or “Holy schist!”

Rock #2: Garnet-Mica Schist.

Rock #3: Garnet-Mica Schist
Another one! But this one is cool because the garnets are much larger. Check out that rhombic dodecahedron garnet at the top of this sample! This was also in my “high school and before” box of rocks, so all I know is that I collected this rock somewhere in New England… probably in Connecticut during a high school geology field trip.

Rock #3: Another garnet-mica schist!

Rock #4: Sandstone Nodule/Concretion
Last but not least, I am sending Danarra a rock that I collected in Petra, Jordan– which may very well be my favorite place in the world. Petra is a remarkable sandstone fantasy world that would be beautiful for the tall sandstone cliffs alone. However, in addition to the impressive geology there are also some very impressive Nabataean and Roman ruins, including remarkable facades carved out of the sandstone. I have visited Petra four times now, but I could visit dozens of more times. Although I am not a sedimentary geologist, I think my dream job would be to study the geology of Petra. Perhaps for a postdoc? We shall see.. I do love desert landscapes.

What is a sandstone nodule/concretion? I actually don’t know very much about these since I’m not a sedimentary geologist- perhaps some of my readers could help? However, I am fairly sure that this rounded sandstone pebble is either a nodule or concretion. I found dozens of these small round sandstone pebbles on the sandy walking paths in Petra. I collected several of them. I have also found very similar sandstone pebbles in Red Rocks Canyon just outside Las Vegas. If anyone knows more about these sandstone pebbles, I would love to read a scientific reference or two. Let me know!

Rock #4: Sandstone nodule/concretion.

Note: At Georneys I also posted some pictures of Petra & Red Rocks Canyon. Check them out at there… I’m having to upload the pictures again here, and I am feeling lazy :-).


Evelyn is a geologist, writer, traveler, and skeptic residing in Cape Town, South Africa with frequent trips back to the US for work. She has two adorable cats; enjoys hiking, rock climbing, and kayaking; and has a very large rock collection. You can follow her on twitter @GeoEvelyn. She also writes a geology blog called Georneys.

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  1. Oh boy, I totally get the late return of books. I procrascinate in reading them ,and soon, I procrascinate on turning them back. Also, I procrascinated on my 15 page research report. Not good. :(

  2. Yeah, I know the feeling about feeling overstressed in grad school as well. But I don’t that I couldn’t be making this happen without support from my friends, so I make sure I schedule time blocks to relax with them, regardless of how busy I am, just so I remember that it’s worth it. I probably should do that tonight….

  3. Awwwwwwww! I figured you just got busy and forgot. Am thrilled you remembered! Will put all four lovely pieces on the Buddha display (aka the shelf the cats can’t get to).
    You ROCK!

  4. I’m shocked no one’s commented about the concretion yet.

    Up here in Alberta, concretions out of some formations in the Western Canadian Sea Board are a treasure trove of invertebrate fossils. The Bad Heart formation, for instance, has a whole bunch of shrimp, crab, and lobster fossils which form the nucleus of the formation, and are often encased in a fairly fine grained sandstone heavily cemented by either quartz or calcite.

    The T-rex fossil excavated in Montana that they reportedly found actual biological material in (while that is still contested) was encased in a concretion, and one of the interesting ideas at the time was to crack open a bunch of other concretion encased dinosaur fossils to see if equivalent biological material has been preserved within, instead of the typical permineralization or replacement types of fossilization.

    I think these two articles are pretty solid in terms of explaining concretion formation:


    Chan, M.A., B.B. Beitler, W.T. Parry, J. Ormo, and G. Komatsu, 2005. Red Rock and Red Planet Diagenesis: Comparison of Earth and Mars Concretions PDF version, 3.4 MB : GSA Today, v. 15, n. 8, pp. 4-10. – Requires a GSA account.

  5. @Danarra:

    You’re welcome!


    Thanks so much for the concretion links! I can’t get the first one to open, but I’ll read the GSA paper this weekend.

    I’m not a sedimentary geologist, but I want to learn more about sedimentary rocks and their features.


  6. The first one is a link to this paper here:

    Calcite-Cemented Concretions in Cretaceous Sandstone, Wyoming and Utah, U.S.A.
    Earle F. McBride, M. Dane Picard and Kitty L. Milliken which specifically discusses the Mokii Balls (the little circular concretions in Red Rocks, Valley of Fire, and various other locales in that horizon.

    Sedimentary geology is pretty cool as well. I think it’s kind of a mutual jealousy hard rock and soft rock geologists have for the other, cuz one of the coolest things I like about hard rock is the huge crystal sizes that only slow cooling at high pressure can allow…

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