This is a short film made by one of my Rockies students as his final project for the class. Enjoy!

Labels: environmental, mining, montana, movies, ore

In October of last year, I presented a list of my favorite analogies for geological processes. Effjot followed up with a visualization of one that was presented in the comments.

Today, I'd like to add to that list with three more evocative analogies.

Hydrothermal disseminated deposits are sweat stains.
Certain types of ore bodies are thought to be "sweated out" from magma chambers as they intrude to shallow enough levels in the crust. The shallow depths have low pressures, and that encourages the magma to devolatilize. The resulting hydrothermal fluids pick up lots of consitituents like sulfur and metals and stream away from the pluton. As they cool off, the dissolved constituents become supersaturated and begin to precipitate out as mineral deposits. These hydrothermal disseminated deposits end up in the pore spaces of surrounding rocks, or filling in cracks. This is kind of like how your body sweats out a solution of dissolved salts in water. When the water evaporates, the salts precipitate out wherever they find the space:

Sills are a funny kind of peanut butter sandwich.
A dike is an igneous intrusion which cuts across local stratification of the host rocks. Sills, in contrast, exploit the weaknesses between strata and inject their magma parallel to bedding. I think of this as being like using peanut-butter-in-a-tube to make a peanut butter sandwich without separating two pieces of bread. Like this three part series:




Exotic terranes are roadkill.
I show the following sequence of images to my Physical Geology students when discussing how exotic terranes accumulate on the leading edge of a drifting continent:








... and I think you get the idea. That one kind of speaks for itself...

How about you? Got any good analogies for relaying geological concepts?

Labels: analogies, art, humor, ore, teaching

And now, a few images from April's Environmental Geology class field trip. We made three stops: (1) a large coal-fired power plant in Maryland, (2) Westmoreland State Park in Virginia to look at coastal erosion, and (3) Prince William Forest Park in Virginia to look at pyrite emplacement and acid mine drainage.

Here's one of the bluffs on the Potomac River at Westmoreland:

Note the recent pile of breakdown in the middle of the bluff where all the water seepage is, and also the orange trail as soil from the uppermost bluff has marked another mass wasting event's passage down to the river.

These are Miocene-aged sedimentary layers known as the Calvert Formation, part of the Coastal Plain. In places, the gray clay has been altered along fracture surfaces, as shown by these orange stripes criss-crossing one another. My toes for scale:


The students spent some time searching for fossils: this is an area where lots of shark teeth are found. We didn't have much luck, but after a long cold winter, it was nice to be standing in the warm sunshine and water:


At Prince William Forest Park, we hiked down to the Cabin Branch Pyrite Mine to look at the massive denudation there due to acid mine drainage, and we also spent some time poking around for treasures, in this case chunks of pyrite:


We had better luck than at Westmoreland...




...But of course we were in a national park at Prince William, so we left the pyrite where we found it. (Westmoreland, in contrast, allows you to keep any fossils you find in loose sediment: that figures, eh?)

I'd like to say that the group of students I had in Environmental Geology this past semester was terrific, one of the best groups I've worked with in a long time. Maybe it was because the class was discussion-focused, or maybe it was the cookies we ate every Tuesday night, but it was a great experience for me, and I'm looking forward to teaching the course again. Thanks, everyone, for making it so much fun!

Labels: coastal plain, environmental, field trips, maryland, miocene, nova, ore, piedmont, virginia

Done with the Cockeysville Marble and fortified with chocolate malts from the Twin Kiss, we ventured on to "Mineral Hill," interpreted as a paleo-black-smoker site from the deep Iapetus. This is a zone of mafic and ultramafic rocks that have been metamorphosed and also mineralized with a suite of sulfide minerals, including pyrite, chalcopyrite, bornite, covellite, and carrollite (in fact, this is the type locality for carrollite). Presumably it was a SedEx-type deposit in the Iapetus Ocean basin. It is geographically associated with the Baltimore Mafic Complex, which is most readily interpreted as a dismembered slice of the Iapetus oceanic lithosphere (that is, an ophiolite). As the Iapetus closed during the Taconian Orogeny, it was accreted to North America and metamorphosed.

The petrology students start picking up pieces from the massive pile of tailings in search of treasures:


Talc shist (soapstone) with malachite:


More of the same:


I forget what this one was, but I loved the "spray" pattern of its bladed crystals:


Chrysotile asbestos:


Pyrite:




And lots and lots of magnetite! These are some of my refrigerator magnets stuck to it:


One more stop to go: the Ellicott City Granodiorite...

Labels: appalachians, maryland, metamorphism, minerals, ophiolites, ordovician, ore

For a few months now, prompted by a comment on one of my blog posts from fellow geoblogger Bryan, I've been listening to the Skeptics' Guide to the Universe podcast. It's pretty darned good. Last week, the team interviewed Seth Shostak, senior astronomer for SETI, who made an offhand statement that there was "plenty of bauxite" on the Moon. Considering that the moon's anorthosite has plenty of aluminosilicate minerals, but none of the tropical rains required to produce a secondary concentration of gibbsite, bohemite, and diaspore, a.k.a. bauxite, I wrote in to compliment the show in general but correct this one small tidbit. This week on the show, they acknowledge my correction, though (of course) they mis-pronounce my name. It starts at 25:35 into the podcast. Ah well -- my own little cross to bear. Glad to help advance human understanding of geological processes!

Labels: astronomy, minerals, moon, ore, podcasts and vodcasts, science and society