From hell's heart I stab at thee: Accretionary Wedge #28

"...to the last I grapple with thee; from hell's heart I stab at thee..."

The Accretionary Wedge challenge for the month is to show off a favorite "deskcrop", those beautiful and significant rocks and minerals that have won a coveted position on the desk of a geologist/teacher. The convergence of the wedge with Halloween added a layer of complexity by asking for spooky items. Well, I have a lot of deskcrops on my desk, so many that there is precious little room for books and office supplies and that sort of thing. It was hard to choose.

That "spooky" thing made it even harder, but what is Halloween about anyway? The day was co-opted by the Christian religion from earlier Celtic traditions, but the upshot of the cultural intermingling of meanings is that on All Saint's Day Eve there are spirits from the underworld set loose on Earth. So I looked for the deskcrop that best exemplifies the underworld, and I realized it could be nothing else but the walls of hell itself: olivine dunite xenoliths from the deep mantle, brought to the surface of the Earth by volcanic eruptions.

Olivine is a beautiful mineral, one of my favorites, with a glassy luster and bright green and yellow color which varies due to a substitution of iron and magnesium in the crystal structure. It is also known as the gemstone peridot, the August birthstone. The streets of Heaven are paved with gold, but the walls of hell are apparently lined with gemstones! The mineral is relatively unstable at the Earth's surface, and readily alters to serpentine when exposed to water in the upper crust.

As for the quote, it comes to us from Moby Dick by Herman Melville, although it was also a memorable quote from the movie Star Trek II: The Wrath of Khan (and I hate to admit that I first knew of it from the movie).

Thanks to Research at a Snail's Pace for hosting the Wedge this month!

Deskcrops!

I've noticed some deskcrops on the geoblogosphere of late, and since I missed one of the early Accretionary Wedges on the topic, I want to "show and tell" some of my deskcrops too. Geologists are notable hoarders and collecters of shiny objects (not unlike crows and packrats), and our desks and workspaces get cluttered quickly. My most treasured single item is a highly crystalline sample of azurite, one of the ores of copper. I'm a sucker for deep blue...

Decades ago in a different job, I was tasked with cleaning out a bunch of old senior exercises in a basement storage area, and a lot of rocks got tossed. This one caught my eye, though, because of the color. The pink crystals are the gemstone tourmaline, and the lavender flakey crystals are a form of lithium-bearing mica called lepidolite. My best guess is that it came from one of the mines in the San Diego region of southern California.

Some deskcrops are not eye-catchers, but have special significance. These bladed crystals are samples of anorthoclase, from the pool of lava on at the summit of Mt. Erebus in Antarctica. It was collected by a researcher who spoke at our campus a few years ago, and was kind enough to donate the samples to the department.

It was kind of hard to choose my favorite deskcrops! The photo above is about a fifth of the total space on my desk, and the rest is similar to this. Books? Not so much. That's what bookcases are for.