In the pink

Sure, diamonds are pretty and sparkly and rare and valuable, but do you know how they form?  Because that's honestly the coolest thing about them.

Diamonds are found in geological formations called kimberlite pipes.  This is a structure shaped like a long, narrow ice cream cone, extending downward into the Earth (how far downward we'll get to in a moment), and characterized by some rocks and minerals you usually don't find lying around -- chromium-rich pyrope garnets, forsterite, and various types of ultramafic (low-silica igneous) rocks that break down to a very specific kind of clay.  Jewel hunters long ago figured out that diamonds were likely to be found in association with these rocks and minerals, and used those as indicators of where to look -- such as the diamond-rich Kimberly region of South Africa (which gave its name to kimberlite), a couple of spots in Greene and Indiana Counties, Pennsylvania, and the Udachnaya area of Siberia.

All of that's just background, though.  Remember how a few days ago, I mentioned how much I'm fascinated with things that are big and powerful and scary and can kill you?  Well, part of the cachet of diamonds is the fact that the way they form is all of the above.

Geologists discovered more or less simultaneously that the composition of kimberlite pipes is consistent with magma found in the (very) deep mantle, and that known kimberlite pipes extend a (very) long way down.  The best models indicate that the eruption that forms them starts on the order of four hundred kilometers below the surface of the Earth, making it the deepest known volcanic feature.

No one knows what triggers the eruption to begin.  It seems to be a rare occurrence, whatever it is.  Fortunately.  Because once it starts, and the magma moves upward through the mantle, the drop in pressure makes dissolved gases bubble out, rather like popping the cork off a bottle of champagne.  This speeds up the movement, which lowers the pressure more, so more gas bubbles out, and so on and so forth.  Also -- gases expand as the pressure drops, so the higher it rises, the more volume it displaces.

The result is what's called a diatreme.  What seems to happen is that with no warning, there's a Plinian eruption -- the same sort that destroyed Pompeii and Herculaneum -- but moving at supersonic speeds.  Imagine what it must look like -- from a distance, preferably -- everything is calm, then suddenly a several-kilometer-wide chunk of land gets blown up into the stratosphere.  The conical hole left behind fills with material from the deep mantle (thus its odd composition by comparison to other igneous rocks).  Give it a few million years, and weathering results in the characteristic clay found in a typical kimberlite.

So what's all this got to do with diamonds?

Well, in the intense heat and pressure of the eruption, some of the carbonate ions in minerals in the magma are reduced to elemental carbon, and that carbon is compressed to the point that its crystalline structure changes to a hexoctahedral lattice.  The result is a transparent crystal that looks nothing like the soft, black, powdery stuff we picture when we think of carbon.  (Further illustrating that bonding pattern is everything when it comes to physical properties.)

Why this all comes up, though, is that not all diamonds are the colorless transparent crystals that usually come to mind in association with the word.  Diamonds actually come in a variety of colors.  Now, on the surface, this isn't that unusual; pure corundum (crystalline aluminum oxide) is colorless, but if it has chromium impurities, it's red (those are called rubies), and if it has traces of iron and titanium, it turns blue (and are called sapphires).  The same is true with beryl (colored varieties include emeralds, heliodor, and aquamarine), spinel, and quartz.

Some diamond colors -- the yellows, blues, and greens -- are due to impurities as well.

The exception is pink.

[Image is in the Public Domain courtesy of photographer Roy Fuchs]

Pink diamonds are really rare, and although they're colored, it's not because they have impurities.  They're pure carbon, just like the colorless ones.  So how do they end up pink?

The clue came from where they're found.  Analysis of pink diamonds showed that they occur in places where kimberlite pipes get caught up in the rupture of tectonic plates.  So it's not just a colossal megaexplosion that's necessary to form them, they then need to get subjected to enormous pressures as supercontinents break up.  Those pressures cause the molecular bonds between the carbon atoms to bend, and that deformation is sufficient to change how the lattice interacts with light, and results in the crystal having a pink color.

Ninety percent of the known pink diamonds come from one place; the Argyle Formation in western Australia.  This area was right on the fault margin during the breakup of the Nuna Supercontinent 1.3 billion years ago.  And the paper that appeared in Nature this week showed that's no coincidence.  Take a colorless diamond, put it in the gigantic vise of a fault during a continental rupture, and it turns pink.

The whole thing is fascinating, not least because producing them requires being in the middle of two of the most violent processes on Earth.  Just goes to show that catastrophic events can result in beauty -- even if you wouldn't want to be in the middle of them as they occur.

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Diamonds in the rough

Sure, diamonds are pretty and sparkly and rare and valuable, but do you know how they form?  Because that's honestly the coolest thing about them.

Diamonds are found in geological formations called kimberlite pipes.  This is a structure shaped like a long, narrow ice cream cone, extending downward into the Earth (how far downward we'll get to in a moment), and characterized by some rocks and minerals you usually don't find lying around -- chromium-rich pyrope garnets, forsterite, and various types of ultramafic (low-silica igneous) rocks that break down to a very specific kind of clay.  Jewel hunters long ago figured out that diamonds were likely to be found in association with these rocks and minerals, and used those as indicators of where to look -- such as the diamond-rich Kimberly region of South Africa (which gave its name to kimberlite), a couple of spots in Greene and Indiana Counties, Pennsylvania, and the Udachnaya area of Siberia.

[Image licensed under the Creative Commons Rob Lavinsky, iRocks.com – CC-BY-SA-3.0]

All of that's just background, though.  Here's the cool part, if (like me) you like things that are big and powerful and scary and can kill you.

Geologists discovered more or less simultaneously that the composition of kimberlite pipes is consistent with magma found in the (very) deep mantle, and that known kimberlite pipes extend a (very) long way down.  The best models indicate that the eruption that forms them starts on the order of four hundred kilometers below the surface of the Earth, making it the deepest known volcanic feature.

No one knows what triggers the eruption to begin.  It seems to be a rare occurrence, whatever it is.  Fortunately.  Because once it starts, and the magma moves upward through the mantle, the drop in pressure makes dissolved gases bubble out, rather like popping the cork off a bottle of champagne.  This speeds up the movement, which lowers the pressure more, so more gas bubbles out, and so on and so forth.  Also -- gases expand as the pressure drops, so the higher it rises, the more volume it displaces.

The result is what's called a diatreme.  What seems to happen is that with no warning, there's a Plinian eruption -- the same sort that destroyed Pompeii and Herculaneum -- but moving at supersonic speeds.  Imagine what it must look like -- from a distance, preferably -- everything is calm, then suddenly a several-kilometer-wide chunk of land gets blown up into the stratosphere.  The conical hole left behind fills with material from the deep mantle (thus its odd composition by comparison to other igneous rocks).  Give it a few million years, and weathering results in the characteristic clay found in a typical kimberlite.

So what's all this got to do with diamonds?

Well, in the intense heat and pressure of the eruption, some of the carbonate ions in minerals in the magma are reduced to elemental carbon, and that carbon is compressed to the point that its crystalline structure changes to a hexoctahedral lattice.  The result is a transparent crystal that looks nothing like the soft, black, powdery stuff we picture when we think of carbon.  (Further illustrating that bonding pattern is everything when it comes to physical properties.)

The reason all this comes up is a discovery described in a press release from the University of British Columbia that I found out because of a friend and loyal reader of Skeptophilia.  Kimberlite pipes are not only unusual, they differ from each other, so the composition of each acts as a geological fingerprint.  So when a UBC geologist named Maya Kopylova tested samples of a kimberlite on Baffin Island, she found that its composition was inconsistent with the rocks of the nearby geological province -- the nearest rocks it matched were in Labrador, almost two thousand kilometers away.

This was sufficient to identify it as part of the North American craton, a (relatively) stable piece of continental crust that currently extends from eastern Canada, through southern Greenland, and over to Scotland.  (It was torn into chunks when the Mid-Atlantic Rift Zone formed on the order of two hundred million years ago, breaking up what was the supercontinent of Pangaea.)

How a chunk of a billion-year-old craton ended up two thousand kilometers away is uncertain, but it does give us a lens into how the continents have shifted during geologic history.  "The mineral composition of other portions of the North Atlantic craton is so unique there was no mistaking it,"  Kopylova said.  "It was easy to tie the pieces together.  Adjacent ancient cratons in Northern Canada—in Northern Quebec, Northern Ontario and in Nunavut—have completely different mineralogies...  Finding these 'lost' pieces is like finding a missing piece of a puzzle.  The scientific puzzle of the ancient Earth can’t be complete without all of the pieces."

Cool, too, that the discovery was made using remnants of what is very likely to be one of the most unpredictable and violent geological events on Earth.  (Okay, the formation of igneous traps is worse.  But still, kimberlites should surely come in second.)  The universe never ceases to fascinate me, and I'm always struck by the fact that no matter how much you know, there's always more to find out.

More, too, to worry about.  Although considering the current state of affairs, a supersonic volcanic eruption might actually lighten everyone's mood.

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Any guesses as to what was the deadliest natural disaster in United States history?

I'd speculate that if a poll was taken on the street, the odds-on favorites would be Hurricane Katrina, Hurricane Camille, and the Great San Francisco Earthquake.  None of these are correct, though -- the answer is the 1900 Galveston hurricane, that killed an estimated nine thousand people and basically wiped the city of Galveston off the map.  (Galveston was on its way to becoming the busiest and fastest-growing city in Texas; the hurricane was instrumental in switching this hub to Houston, a move that was never undone.)

In the wonderful book Isaac's Storm, we read about Galveston Weather Bureau director Isaac Cline, who tried unsuccessfully to warn people about the approaching hurricane -- a failure which led to a massive overhaul of how weather information was distributed around the United States, and also spurred an effort toward more accurate forecasting.  But author Erik Larson doesn't make this simply about meteorology; it's a story about people, and brings into sharp focus how personalities can play a huge role in determining the outcome of natural events.

It's a gripping read, about a catastrophe that remarkably few people know about.  If you have any interest in weather, climate, or history, read Isaac's Storm -- you won't be able to put it down.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Diamonds, water, the Great Flood, and car wrecks

When I was thirteen years old, I witnessed a car crash in front of my parents' house.

It was a bright red convertible, going far too fast -- and the driver was not quite able to negotiate the curve that the road made right by our driveway.  The car hit a road sign, went airborne, flipped in midair, and skidded down the hill in the neighbor's yard on its top.

My dad and I ran toward it, knowing that the likelihood was that there was a severely mashed human underneath.  But amazingly, this was the one-in-a-million situation where not wearing a seatbelt had saved the driver's life.  He'd been thrown clear, and came away with no more than cuts and bruises (and a totaled car).

But what I remember about this incident most of all is the feeling of complete helplessness -- watching the car careening down the road, seeing it launch itself into the air, being certain at the time (although I was happily proven wrong in the end) that that driver was seconds from his death.  To this day, I still have this feeling when I see something rushing toward an outcome that I am powerless to prevent.

It's an intensely uncomfortable sensation.

I experienced this feeling just yesterday, albeit in a less life-threatening situation, when I ran into a seemingly innocuous story over at the BBC News Online entitled, "Mineral Hints at Bright Blue Rocks Deep in the Earth."  In it, we hear about the discovery of inclusions of a mineral called ringwoodite in diamonds that had formed deep in the Earth (an estimated 600 kilometers underneath the Earth's surface).

[image of a ringwoodite crystal courtesy of photographer Jasperox and the Wikimedia Commons]

"Diamonds, brought to the Earth's surface in violent eruptions of deep volcanic rocks called kimberlites," the article states, "provide a tantalising window into the deep Earth.  A research team led by Prof Graham Pearson of the University of Alberta, Canada, studied a diamond from a 100-million-year-old kimberlite found in Juina, Brazil, as part of a wider project."

So far, something of interest only to geologists.  But then the article went on to explain one of the odd things about these inclusions:

"While ringwoodite has previously been found in meteorites, this is the first time a terrestrial ringwoodite has been seen. But more extraordinarily, the researchers found that the mineral contains about 1% water.  While this sounds like very little, because ringwoodite makes up almost all of this immense portion of the deep Earth, it adds up to a huge amount of deep water...  They also provide the first direct evidence that there may be as much water trapped in those rocks as there is in all the oceans."

And that's when I saw the impending car crash.

"A key question posed by the observation," the article continues, "is to understand the extent to which plate tectonics on Earth leads to oceans of water being recycled deep within our planet, and to predict the likely amounts of water trapped in other rocky planets."

No, no, stop, please stop...

"Prof Joseph Smyth of the University of Colorado has spent many years studying ringwoodite and similar minerals synthesised in his laboratory.  He said: 'I think it's stunning! It implies that the interior may store several times the amount of water in the oceans. It tells us that hydrogen is an essential ingredient in the Earth and not added late from comets.'"

Too late.

You do see where this slow-motion auto accident is heading, right?  Let me make it clear by posting three of the comments that showed up when the story, in somewhat abbreviated form, made its way onto The Daily Mail:

The Christian bible has some things to say about incredibly large amounts of water deep within the earth. KJV Genesis 7:11 Noah, his family and the creatures, enter the ark 11 In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened. KJV Genesis 8:2 The waters subside 2 The fountains also of the deep and the windows of heaven were stopped, and the rain from heaven was restrained; KJV Proverbs 8:27-29 27 When he prepared the heavens, I was there: when he set a compass upon the face of the depth: 28 When he established the clouds above: when he strengthened the fountains of the deep: 29 When he gave to the sea his decree, that the waters should not pass his commandment.

This water was mentioned in the bible when it told of God making all the water below the earth rise and flood the world. Read about Noah. Believe what the bible teaches us. Your soul is at stake.

"....all the fountains of the great deep burst open, and the floodgates of the sky were opened. And the rain fell upon the earth for forty days and forty nights. " Genesis 7:11 cf John Lennox Mathematician Oxford U. It is certainly scientific to believe in God, and really now, what sort of spirit promotes hatred for people who do?

Then some poor slob, who hasn't figured out yet that arguing in the "Comments" section of popular media is completely pointless, responded that in order to believe the biblical account of the Great Flood, you'd have to accept that it rained enough in "forty days and forty nights" to cover the entire surface of the Earth, a quantity he calculated as 2000 million cubic kilometers of water.  (I haven't checked his math, but it doesn't seem to be off by much, given that the surface area of the Earth is 510 million square kilometers.)

 

To no avail.  Of course.

[1] Direct your free water clarifications to the DM which created the headline, "Revealed:The vast reservoir hidden beneath the Earth's crust that holds as much water as ALL of the oceans." [2] You say, "2000 M cubic km of water fell as rain." Where does the bible say that? Read Genesis 7:11 again. It specifically mentions the breaking up of the fountains of the deep along with the windows of heaven being opened up. This implies that all the water did not come from rain. Besides providing the source for your claim, please show your calculations along with your assumptions. [3] You don't know and can't prove that these bible stories are myths anymore than you can definitively show what a photon is or what gravity is. Neither can you prove by testable replication where and how life originated and diversified. You are as powerless to explain these things as you are to definitively reject these verses in the bible.

So if the initial publication of the article led me to feel like I was watching the beginning of an intellectual train-wreck, the aftermath left me doing repeated headdesks.

And just because I feel obliged to say it:  no, the discovery of a great deal of chemically-bound water in the mantle transition zone does not support the biblical flood story.  For one thing, the rocks down there are at at temperature of about 1600 C, so if god "broke up the fountains of the deep," what would come out is not pure, clear water, but a huge gusher of extremely hot magma.  No, there is nothing even remotely possible about a Great Flood Covering the Earth, not to mention the whole Noah's Ark nonsense.  In order to accept any of that as literal fact, you either have to be (1) ignorant, or (2) engage in confirmation bias to an extent that is truly mind-boggling.

And to the scientists who published this research; I know you were just trying to do some cool geology.  I know you were excited by your find, and what it might tell us about the chemistry of the Earth's mantle.  But we skeptics already spend way more of our time than we should arguing against the biblical literalist lunatics, and trying to stop them from spreading their nonsense into public schools -- and now they think they have some scientific support for their Bronze-Age mythology.

Yes, I know it doesn't really support their beliefs, but they think it does, and as a result we're going to be hearing about it for the next ten years.  And for that, I don't know if I can ever forgive you.