Monday Geology Picture: South African Wind Farm

A wind farm near Jeffrey's Bay, South Africa. — A wind farm near Jeffrey’s Bay, South Africa.

South Africa is currently facing a significant shortage of electricity. Recently, there have been regular periods of “load shedding” or planned power outages. Basically, there is often not enough power to go around, so the power is purposely turned off on a rotating schedule. In the neighborhood where I live and work in Cape Town, the power is regularly turned off for two hours a day or sometimes for four or more hours per day. As you can imagine, these regular power outages are quite disruptive to work and home life and certainly have a negative impact on the economy.

There is a great need for more power sources here in South Africa. Thus, I was quite pleased when I recently drove past a relatively new wind farm near Jeffrey’s Bay, South Africa. As the wind turbines spun, I smiled thinking about the power that they are diligently producing. Although wind farms will probably only play a small role in solving South Africa’s energy crisis, every little bit helps. Also, every megawatt of power produced by a wind farm is one less megawatt of power than needs to be produced by “dirtier” carbon emitting power plants, such as coal plants.

Monday Geology Picture: Listwanite Hills in the Sultanate of Oman

OLYMPUS DIGITAL CAMERA — Listwanite hills in the Sultanate of Oman, January 2012. The reddish parts of the moutnain are listwanites while the grayish parts are less-altered peridotites.

Today I am going to share some pictures of listwanite (also sometimes spelled listvenite, listvanite, or listwaenite), an unusual rock type that I bet even some of the well-educated geologists who read this blog have never seen or even read about. I don’t even think there’s a wikipedia entry about listwanite. Perhaps I’ll write one after my thesis defense next month.

Listwanite forms when ultramafic rocks (most commonly mantle peridotites) are completely carbonated. The pyroxene and olivine minerals found in peridotite commonly alter to form carbonate and serpentine minerals. However, peridotites are usually not completely carbonated. Rather, they typically contain carbonate veins (primarily magnesite; also calcite, dolomite, and other carbonates). Complete carbonation of peridotite means that every single atom of magnesium and calcium as well as some of the iron atoms has combined with CO2 to form secondary carbonate minerals such a magnesite and calcite. The silica atoms in listwanite are found in quartz. Thus, liswanites consist of quartz (a rusty red color) and carbonate and also sometimes talc and Cr-muscovite (a mineral known as mariposite/fuchsite). Geologists are still studying how listwanites form, but they likely form through the interaction of CO2-rich fluids with peridotites at higher than ambient temperatures up to ~200 degrees Celsius. Structural controls (faults and fractures) permit the percolation of the CO2-rich fluids through peridotite, so the formation of listwanites is generally structurally controlled.

Listwanites are important rocks to study for a number of reasons. First of all, listwanites contain large amounts of CO2 which originated from fluids and which is now stored in solid mineral form. Recently, geologists and other scientists have been investigating the potential of storing CO2 in solid minerals (which are more stable than CO2 stored as a liquid or gas) through carbonation of mafic and ultramafic rocks (see, for example, this Nature Geoscience Progress Article by Matter and Kelemen, 2009). Mafic and ultramafic rocks uptake significant CO2 through their natural alteration processes (that’s what I study for my PhD, so expect more on this in the next year or so as I submit my papers for publication). However, the natural carbonation rates of these rocks are too slow to significantly offset anthropogenic CO2 emissions. Therefore, scientists are currently investigating if it is possible to geoengineer CO2 uptake in mafic and ultramafic rocks so that this CO2 uptake happens more quickly. This could be done, perhaps, by fracturing and heating and injection of CO2-rich fluids. This is already being tested in mafic basalts through the CarbFix Project in Iceland.

However, scientists and engineers still have plenty of work to do in order to figure out the right conditions and protocols for CO2 sequestration in mafic and ultramafic rocks. In order to learn about what conditions lead to complete carbonation of ultramafic rocks, scientists such as Peter Kelemen and Gregory Dipple (and their many grad students and collaborators) are working to learn more about listwanites to see if mother nature can provide some clues.

In addition to the recent interest in listwanites for carbon sequestration efforts, listwanites are also important because they are often associated with economic mineral deposits, particularly gold deposits.

So, now that I’ve explained what listwanites are and why they are important, here are some pictures of listwanites which I observed during my trip to Oman back in January. Listwanites are pretty neat rocks, aren’t they?

Blast from the Past: Carbon Cycle Story

Atom Unit Report Booklet.

I’m finishing up my packing this weekend, so that means it’s time for another “Blast from the Past” post. This is a story narrated by a carbon atom going through the carbon cycle. This story comes from my “Atom Unit” report booklet. Last week I shared a story called “Element Talk Show” with you from this same booklet. Just this evening I noticed that I wrote the date on the back of the booklet. I wrote this booklet in 1994 when I was ten years old and in either 4th or 5th grade.

This is another nerdy, weird story, but at least I had a pretty good understanding of the carbon cycle for a ten-year-old. All spelling, grammar, and punctuation are original.

The Life of a Carbon Atom:

The Atmosphere:
My life started out easy, in the air. I had the pleasure of being in a molecule with two extremely nice oxygen atoms. I just drifted in the air, happy that I had my full supply of electrons. Perhaps I should introduce myself. I am a typical carbon atom with six electrons. I now am in a carbon dioxide molecule and am just drifting. I waved to my friends, oxygen gas, a molecule of two oxygen atoms (I find oxygen the nicest atom), and nitrogen gas, a molecule of two nitrogen atoms. All of us are in our gas form. I’ve heard stories of becoming solids and many different things, but now I just like the aaaaaaaaaaaaair*. I was being sucked in by something, I was leaving the air. “Goodbye!” my friends yelled, “you’ll like being a solid. Good luck.”

The Plant:
It turned out I was being breathed in by an eggplant. It wasn’t bad being an eggplant, but I prefer being in the air much better. I was in the eggplant for several days. One day the eggplant was picked. I was relieved because it was turning into cold weather and at night frost reached its arms over the eggplant. I remember being put in an icebox and staying there for a day or so. This cold was not like the cold of the frost, but a more gentle concentrated cold.

“Ray, get some eggplants out, Marilyn is going to have company tonight.”

“Not eggplant tonight, Martha. You know Marilyn doesn’t favor eggplant,” he replied.

“I never asked her to eat any. Will you just get ’em out?”

The icebox door opened and I was lifted out and set on a table. The eggplant was cut up into little slices, myself being part of the smallest slice. I was placed on the table with some parsley and the rest of the eggplant. There was not just eggplant on the large white table, but turkey, corn, rolls, butter, salad, potatoes, salt, pepper, napkins, plates, spoons, forks, knives, salad forks, roast beef, and some other things that I haven’t any idea what they are. One of the best things on the table was fried yams.

“Martha! Martha! Where is that producer I invited for dinner? He’s Late! I’m eager to sign that contract,” Marilyn complained.

“Hello,” a famous hollywood producer walked into the dinning** hall, “this must be Marilyn, Marilyn Monroe.”

“Of course I’m Marilyn Monroe. Who do you think I am? Now what about that contract? Pass the eggplant please.”

I felt the eggplant being bumped around on the platter. A fork was lifted and the eggplant was eaten by Marilyn Monroe!

The Human Body:
Shining white sharp teeth chewed the eggplant and then Gulp! A long dark passage led straight downward into a larger space called the stomach. I was bumped around and jumbled about. I was not in the human body for long. It was just a couple of hours***. Just as Marilyn Monroe was about to turn out the light for the night, eager to start work on her new movie she took a deep breath, and I caught sight of two very nice oxygen atoms. I had been a bit cranky without my full eight electrons and I was eager to join them. So I did and Marilyn Monroe breathed me out as carbon dioxide.

The Atmosphere Again:
I was free! Happy, in the atmosphere again. I came to know my two oxygen atoms and was very happy in my new molecule. I stayed in this molecule for a few years, floating around and having the time of my life. My molecule rested near the ground, maybe too close because sooner than I knew it I was being sucked up by the roots of some plant.

Rain Forest:
The roots belonged to some berries. These berries nested in the middle of a vast rain forest. I heard some birds tweeting around me. A leopard pounced on something, catching his prey. I stayed in this plant for a million years or so (I really just lost count) until eventually it was pressed and compacted so much that I turned into a different substance altogether. I still lay in the rain forest until I heard the noise of shovels digging up the ground above me. Finally after such a long time light shone around. For the first time I saw what I was.

Coal:
“This is is it Ricky, coal. We’ll haul in a good bundle for this lot.”

“Would you be quiet? You’re forgetting we have to use some of this in our own research. We’ll sell the rest though. Help me get this out of here.”

I felt bits of coal being lifted up and put into a weird carrier type thing. It was really a compartment of their space mobile used for storing items that were not needed until their next stop.

“What should we try now?” a strange voice asked.

I had been in the coal that had not been sold and now scientists were staring at me through advanced equipment.

“Lets try burning the coal. Ancient Americans often used this process to heat things, but it was most commonly used for cooking things. We are going to take this recreation of what they called bacon and try to cook it in coal and in order to do that we must burn the coal.”

And so I was burned and set free by it. I mixed with oxygen and became carbon dioxide. I was free for the present, but soon I would be in a human or plant. I would never be free from the carbon cycle.

*I think I transcribed the correct number of “a”s here.

**Hee hee first “dinner” now “dinning hall.”

***Not sure about the science of this, but since this is a story narrated by a sentient carbon atom, I’ll roll with it.

My interest in the carbon cycle has continued to adulthood. For my PhD thesis, I study the formation of carbonate rocks in mantle peridotite in the Samail Ophiolite in Oman. These carbonates form when mantle peridotite interacts with carbon dioxide (CO2) and alters to form solid carbonate minerals. Alteration of mantle peridotites to carbonates is a process that naturally removes CO2 from the atmosphere and hydrosphere and stores this CO2 in solid mineral form. So, we call this process a natural “carbon sink” or natural “carbon sequestration.” Understanding natural CO2 storage in carbonate rocks may help geologists and engineers figure ways to artificially store CO2 in carbonate rocks as a way of offsetting anthropogenic CO2 emissions. Today, my understanding of the carbon cycle is slightly more sophisticated than my understanding when I was ten, but, hey, you have to start somewhere.

The carbon cycle is a little more complex than the above story indicates. Perhaps I should write a new story in which the carbon atom cycles through even more reservoirs. For instance, the carbon atom could spend some time in an ocean foram and in a carbonate vein in one of my Oman peridotites. If the carbon atom goes through every possible reservoir, the story could be very long indeed.

Here are a couple of figures showing the carbon cycle:

First, a pretty one from wikipedia: