Saturday, May 28, 2011

Weird Geology: Name That Rock Type!

Note: AW #34, Weird Geology, has now been accreted at En Tequila Es Verdad.

This month's Accretionary Wedge topic, hosted by Dana at En Tequila es Verdad, is one near and dear to my heart: weird geology. To step back a bit, one might define weird as something decidedly outside or beyond typical human experience. Taking that as a working definition, nearly all geology is weird: the environmental conditions, rates of change, chemical reactions, as well as starting materials and end products are too hot, too high pressure, too slow, too extreme, too unusual, or too obscure to make sense without quite a bit of background. Conversely and paradoxically, the materials and processes are often so mundane that we simply don't notice them or pay attention to them. Just as the structures and behaviors of a spider or flowering plant are so day-to-day that few really look hard and try to understand these odd (from a human perspective) organisms, so too the never-ending passage of sand, silt, mud and dissolved material through a neighborhood stream goes unnoticed and unremarked. Yet millennia and eons of such mundane activity will result in breath-taking changes in the nearby landscape. From this perspective, I think it's fair to say that nearly all geology would be considered weird to most, and certainly to those with no training or background in the subject.

I think of myself impossibly lucky in that even with a considerable background, I can still look upon geologic processes and materials with such fresh eyes, and see the wondrous weirdness of such things with one part of my mind, even as I observe, analyze and hypothesize with another. Perhaps it's schizophrenic, but it pleases me to be amazed by things that generally make pretty good sense to me.

All that said, there is a matter of degree... there are definitely some rocks and processes that are more difficult to come to grips with. For example, I'm fascinated by komatiitite, a type of volcanic rock characterized by its extremely high magnesium content. It can be considered the volcanic equivalent of peridotite, just as basalt is the volcanic equivalent of gabbro. It was quite abundant in the earth's early history, but as the planet has aged and cooled, as its original dole of radioactive nuclides has decayed and decreased, the geothermal gradient has become too gentle to allow melts of this composition to reach the earth's surface. One can think of komatiite as an "extinct" rock type. It is preserved as lithic "fossils" in various places (I have had the opportunity to see some first hand in the Hill Lake quad between Temagami and Cobalt, in central Ontario), but not only is it no longer created, it no longer can be created.

But the weirdness I really want to address gets at the way we name things. Often, the way we do science can get in the way of better understanding- a characteristic shared with language generally. Words allow us to symbolize ideas we can share with others, and allow us to perform abstract operations on the symbols that we could not perform with the actual thing. But the utility and availability of those symbols also confines us. We tend not to think too much or too hard about things for which we do not have words.

Anyone who has had even a grade school lesson or few on geology knows the three rock types: igneous, metamorphic and sedimentary. A little more background, and one begins to grasp just how arbitrary the boundaries between those rocks types are, and how difficult it is to simply draw lines between them. Exactly how hot, and under how much pressure, must sedimentary rocks be, before miniscule changes in textures and mineralogy force us to conclude that the rocks must be considered metamorphic? In fact there isn't, nor can there be, any such precise definition. We learn to hedge; we create a new facies ("zeolite grade metamorphism") to delineate this intermediate stage. Never mind that the vast majority of zeolites and zeolite-cemented rocks I have dealt with are clearly the result of diagenesis, not metamorphism.

But at least we can assign all known rocks to those three classes, or their intermediaries, right? Well... maybe not so much. The term "metasomatic rocks" came up in only one of my classes, and only in passing. The term was not used at all in my economic geology class, where most of the rocks we discussed could be considered to be members of that group. The roots (meta=change, soma=body) imply a change in mass composition, differing from a common assumption in metamorphism, that the bulk composition of the rock is mostly fixed, but mineral phases and textures change in response to changing T & P. With metasomatic rocks (AKA hydrothermal rocks), certain elements/ions may be preferentially removed or deposited as their solubilities change due to changing temperature of transporting water/water vapor/hydrothermal fluid. Even the concept of liquid and gas become fuzzy at high enough temperatures and pressures. For example, above a temperature of about 375 C, water behaves as a gas; at or slightly below that so-called critical temperature, it requires a pressure of 218 atmospheres to maintain a liquid state. So what happens if both T and P exceed those values? You have what is called a supercritical fluid, one which has a density nearly that of liquid water, but a behavior more like that of a gas. And one that is very, very reactive with many minerals. A graph of SiO2 solubility (both quartz and amorphous silica) can be seen here (~500 kB PDF). Note that under the conditions we are accustomed to, SiO2's solubility is essentially zero; somewhere around 325-350 C, it hits a maximum of about 600 PPM for quartz to 1600 PPM for amorphous silica.

I do not currently have any photos of vein quartz, so I snagged this one from Callan's class notes for Geol 135; follow the link for a full description, about halfway down the post.
So should this quartz vein be considered igneous, metamorphic or sedimentary? It crystallized from a hot, silica saturated fluid, like an igneous rock, and the textures are most similar to igneous textures. But that fluid was water, so perhaps it should be considered a chemical sedimentary rock. On the other hand, the conditions of high T & P are suggestive of metamorphism, and the mineralogy is more like metamorphic rocks than most we would consider igneous or chemical sedimentary. How do we resolve this conundrum?

This is not a trivial question. While metasomatic/hydrothermal rocks are fairly uncommon, I would not really consider them rare. And while (taking an educated guesstimate) I suppose they probably make up a fairly small fraction of a percent of rocks exposed on the planet's surface, they are extremely important economically. The same processes that dissolved quartz from one region and redeposited it in concentrated form in the vein above can do exactly the same thing with a variety of other materials and elements. Think gold, copper, silver, zinc, lead, barium, and many, many others- our sources of these materials are largely places where moving hot water has concentrated them to a degree and in a location where they can be extracted profitably.

I don't have a sense that there is widespread acceptance of "metasomatic rocks" as a valid class at the same level as the big three, but at least one person (I think it was @stressrelated, but I'm not positive) has said the text they use considers that class as a fourth rock type.

So that gets all the unrecognized rock types, right? Well, maybe not so much. Again, as always, I cannot speak for the geologic community; I can only say I've spent some time thinking about this and toss my ideas out there. If anyone finds them useful, super! If they need to be criticized or shot down outright, I'm open to hear/read the reasons. But I would suggest there are at least two more rock types that we may need to consider. The first is vanishingly rare, the second fairly common but short-lived, in the earth environment. And since there are not widely accepted words for these rock types, I have to give them my own names: let's call them sublimate and cryologic rocks.

Sublimate rocks would be those that crystallize directly from a gas to a solid. On earth, sulfur is probably the most important sublimate rock (though most of it is mined from and resides in other rock types). The Big Picture had a striking gallery a couple of years ago of sulfur mining in Indonesia; I'm pretty confident that most of the sulfur condenses from fumerolic gases- though some may have remelted, and would thus be considered igneous. But thinking about the still bigger picture, if my understanding is correct, nearly all the solid matter in our solar system was originally gaseous effusions from an earlier generation of stars. Those gases crystallized to form dust and chondrules, the primordial building blocks of the terrestrial planets. So while sublimate rocks and minerals may be of miniscule importance on earth today, understanding them may be of fundmental importance in comprehending the history of our solar system and our home.

Cryologic rocks would be those that are made of frozen material that would be gas or liquid under the conditions with which we're most familiar. The biggest deposits of these on our modern world are in Greenland and Antartica: ice. But again, many moons from Jupiter outward have a large component of frozen water, ammonia, and hydrocarbons. Recognizing and understanding this rock type and the kinds of processes, chemical reactions and depositional patterns that can occur in it will be of critical importance to understanding what has happened and is happening today in the cooler parts of our solar system.

I'd like to develop this more, but it's already late: it was due yesterday. I'm tired and exasperated with Firefox, my computer and the Interzone Wifi. I'm going home, where I haven't had a wifi connection for a few weeks. But I hope this tweaked your imagination a little, and made you think about the idea that I mentioned near the beginning: that naming things is very useful and very powerful, but it can become limiting when you feel as if you've named everything important. You probably haven't, and if you don't have a word for it, you will tend to be blind to it.

How many rock types have yet to be named?

Saturd80's

The Vapors, Turning Japanese:

B-52's, Rock Lobster:

XTC, Senses Working Overtime:

Thursday, May 26, 2011

Wednesday, May 25, 2011

RIP Spirit

There have been numerous reports over the last couple of days on the fact that after many attempts, NASA is giving up on re-establishing contact with the Spirit Rover. Phil Plait at Bad Astronomy provides what strikes me as a very fitting eulogy. Followup: Another concise but satisfying summary of the life and times of Spirit by Ryan Anderson at The Martian Chronicles.

I got quite a bit of flack, early in Spirit's rovings, for pointing out that it was very slow, primitive, and limited. I stick by those comments, though. With a six-hour source of breathable air, a hammer, hand lens and camera, I could accomplish in that time much of what Spirit took six years to do. What my critics failed to grasp was that this was intended as a slam on neither the rover, its engineers, nor the mission scientists who managed the day-to-day logistics, data acquisition and analysis. The fact is, we do not have the means to put me (or others more competent) onto Mars alive. Spirit was state-of-the-art... ten years ago. My point was simply that compared to technologies of the near future, or (drool) human explorers, it's important to understand just how limited Spirit really was. That should take nothing away from the accomplishments of the plucky little rover that could, but rather provide motivation and inspiration for the next steps in our exploration of Mars and other solid-surfaced planets and moons.

To Paraphrase the X-Files, the truth is out there, and I want to believe we have the determination to find it. I know we have the resources. I know if we choose to, we can figure out how to make it happen. The only thing I'm uncertain about is whether we have the will.

Certainly, taking the next step will help make up for the undignified manner of Spirit's demise:

Wednesday Wednesday

From Forbidden Planet, accompanying an article claiming that Tim Burton is going to do a stop-motion Adams Family film. The post is more than a year old, and I haven't heard anything else about it, so I'm dubious.

Don't Panic, It's Towel Day

Shoot, almost missed this. I looked it up earlier in the month, and somehow got it into my head it was on May 28th. Thankfully, someone else mentioned it was Towel Day, I double checked, and so it is! For better or for worse, I had been seriously considering draping a towel around my neck for the occasion, and I haven't. Maybe next year. For this year, though, no sheepish explanations that I am indeed a serious nerd.

Tuesday, May 24, 2011

Tuesday Tits

Marsh tit, Poecile palustris, from Wikipedia.

Monday, May 23, 2011

Introducing Bif

Three months ago, I got a new kitteh, Bif, and I wanted to post some pictures of him for the GeoLOLCat meme that's going around.
This first one was taken his first night in my apartment; a beanie baby toy that had been given to me at Christmas of '09 is still one of his favorite toys. As you can see from the rest of the photos, he's filled out quite a bit since February.
Posing with a rock hammer...
Suspiciously watching me watch Jurassic Park...
Trying to figure what the heck I'm up to with that danged string...
And sleeping by the porch door. Why Bif? Well, it's a nice, trite male name, and when he arrived, I was struck by his fine stripes, which reminded me of laminated sediments. Shift the color balance to extreme red, and...The LOL's I've done of Bif can be seen at the GeoLOLCats post.

Moonday: Io

It has been my intention to draw attention primarily to moons that aren't as well known or "popular" in this series, but this image from yesterday's APOD takes the cake:(follow the link to the site and click the pic there for full-size awesomeness and detailed insets) Quoth APOD:
What's happening on Jupiter's moon Io? Two sulfurous eruptions are visible on Jupiter's volcanic moon Io in this color composite image from the robotic Galileo spacecraft that orbited Jupiter from 1995 to 2003. At the image top, over Io's limb, a bluish plume rises about 140 kilometers above the surface of a volcanic caldera known as Pillan Patera. In the image middle, near the night/day shadow line, the ring shaped Prometheus plume is seen rising about 75 kilometers above Io while casting a shadow below the volcanic vent. Named for the Greek god who gave mortals fire, the Prometheus plume is visible in every image ever made of the region dating back to the Voyager flybys of 1979 - presenting the possibility that this plume has been continuously active for at least 18 years. The above digitally sharpened image of Io was originally recorded in 1997 from a distance of about 600,000 kilometers. Recent analyses of Galileo data has uncovered evidence of a magma ocean beneath Io's surface.
Regarding that magma ocean, which I also mentioned last Moonday, Erik Klemetti had a good clarification last Wednesday on why "ocean" is probably not the best word to use to clearly communicate the nature of magma in Io's subsurface.

A couple of other loony images have come across the innertubz recently: the first is another APOD from May 12 of Enceladus and its cryovolcanism, which I had actually been intending to use for last week, until I got distracted by the Callisto/Callista differentiation. The second came from The Cassini Solstice Mission webpage this morning, and captures five of Saturn's moons in one frame!
Rhea (1,528 kilometers, or 949 miles across) is largest here and is closest to Cassini. Dione (1,123 kilometers, or 698 miles across) can be seen just above the rings near the center of the image. Tiny Prometheus (86 kilometers, or 53 miles across) is just barely visible in the rings to the right of Dione. Epimetheus (113 kilometers, or 70 miles across) is to the right of the rings, and Tethys (1,062 kilometers, or 660 miles across) is on the extreme right of the image.
I've linked the full-size image here; the only one that might be difficult to spot is Prometheus, which looks more like a tiny bump on the ring plane, rather that a moon, just to the right of Dione.

Sunday, May 22, 2011

I Survived the Rapture, And All I Got Was These Stupid Sunday Funnies

What a week! In addition to all the regular stuff, there was, of course, the eminently snarkable end of the world. If you've seen 2012, you know that that is fucking laughable.epic4chan
TYWKIWDBI
Clay Bennett
Oh dear God... there oughtta be a law. Skull Swap
God Hates Protesters
Sofa Pizza
Peanutweeter
BizarroBlog
Breaking News of the Day: Donald Trump Won't Run
see more The Daily What
4koma comic strip - Podiatrists Really Have a Great Sense of Humor
see more Comixed
funny puns - The Only Thing That Makes Kerouac Good...
see more So Much Pun
funny celebrity pictures - LASER POINTER
see more Lol Celebs
Tree Lobsters
Savannah Cat and Fennec Fox Gif - Savannah Cat and Fennec Fox
see more Gifs Savannah cat and fennec fox... so Cute!
demotivational posters - GAH
see more Very Demotivational
Peanutweeter
Dork Tower
Bits and Pieces
epic4chan
funny graphs - It's Okay, You Still Have Alfred
see more Funny Graphs
Funny Pictures - Cat Gifs
see more Lolcats and funny pictures
funny celebrity pictures - Prom Night on the Enterprise
see more Lol Celebs
Peanutweeter
funny puns - But the Results Are Often Quite Non-Linear
see more So Much Pun
Big Fat Blog
demotivational posters - NUCLEAR FUSION
see more Very Demotivational... Actually, what puzzles me is where in the Bible it says there's oxygen in space.
Diet Coke and Mentos: Together At Last Gif - Diet Coke and Mentos: Together At Last
see more Gifs "Diet Coke and Mentos: Together at Last."
Via Bits and Pieces
Calamities of Nature
Classic: Dang Human Gif - Classic: Dang Human!
see more Gifs
Sloth Getting Some Help Gif - Sloth Getting Some Help
see more Gifs... Woah! That was a rush!
4koma comic strip - Makes the Most Sense
see more Comixed
Sign Of The Times of the Day
see more The Daily What
Nedroid
Bits and Pieces
funny celebrity pictures - not the first time
see more Lol Celebs
demotivational posters - It's Not Over Yet, Kids
see more Very Demotivational
Tree Lobsters
Sober in a Nightclub
Funny Pictures - Emo Alpaca
see more Lolcats and funny pictures... as you wish...
Before And After Alpaca of the Day
see more The Daily What
The Far Left Side
The Far Left Side
Clay Bennett
funny celebrity pictures - I LOVE TO PLAY WITH MYSELF
see more Lol Celebs... seriously though, who doesn't?
The Daily What (click the pic to embiggen)
One from a very large set of funny signage at Dark Roasted Blend
xkcd
Fake Science
Sofa Pizza... the Charlie Brown of the Cretaceous
Sofa Pizza
The High Definite
epic4chan
epic win photos - Rapture Hours WIN
see more Hacked IRL - Truth in Sarcasm
epic4chan
Morning Links
see more The Daily What. It's not a huge deal, but I do wish that captions could live up to first grade spelling standards.
Bits and Pieces
Bits and Pieces
Sober in a Nightclub
Scaredy Cat Gif - Scaredy Cat
see more Gifs. Betcha didn't know cats could fly, didja?
Cyanide and Happiness
Sober in a Nightclub
funny graphs - Sunny With a Chance of Rapture
see more Funny Graphs
Sober in a Nightclub
Sober in a Nightclub
Sign Of The (End) Times of the Day
see more The Daily What
Just an Earth-Bound Misfit
One of a large collection of "rapture bombs" at EpicPonyz, and another from the same set:Blackadder
ChannelAte
epic4chan
How many puppies can you count? I didn't even try. Bits and Pieces
4koma comic strip - It Gets You Everywhere You Need to Be
see more Comixed
Cyanide and Happiness
What Would Jack Do?
The Daily What