@earthstory / earthstory.tumblr.com
Kimberlite Kimberlites are volcanic eruptions that start deep inside Earth’s mantle, at depths of hundreds of kilometers. At that depth, carbon dioxide may not easily fit into the available minerals, and might instead sit as a (supercritical) fluid, in-between larger mineral crystals.
The 442 carat diamond found at the Letseng mine in Lesotho in August 2020. Created millions of years ago deep in the earth, these things were blasted to the surface in violent volcanic explosions which also occurred millions of years ago.
Hands up if you’d like a diamond for a few dollars? The Crater of Diamonds located in Arkansas, USA allows you to be the miner and search for diamonds, and then keep any you find. The Crater of Diamonds was first discovered by J. Huddlestone in 1906 who spotted odd crystals in his soil. Since then 30,000 diamonds have been found in the park by some of the 3,000,000 visitors each year. With prices of $10 for adults and $6 for children aged 6-12, it's a fun family day out!
The biggest water cycle As I'm writing this, there are a handful of puffy white clouds in the sky above me. Clouds are part of the water cycle that we experience every day – water evaporates from the oceans, moves around the atmosphere, comes down as precipitation, and makes its way back towards the ocean through rivers, lakes, and groundwater.
The Worth(lessness) of Diamonds and the Building of an Empire
The diamond pictured here is a 101.3 carat stunner, sold for a record-breaking $26.7 million in 2013. The real worth of this rock though, is pretty well nothing.
The marketing of the diamond industry was, and still is, pure genius. As the Chairman of De Beers, Nicky Oppenheimer, said himself: "Diamonds are intrinsically worthless." Let's begin with some history/geology: What is a diamond? Simple: pure carbon. A diamond is elemental carbon in its densest Earthly form. What makes diamonds so strong is the arrangement of those carbon atoms, which form a complex lattice. The lattice shape also prevents impurities much better than other atomic arrangements. Some impurities still happen, of course, which results in the rare colours, for example: yellow = nitrogen, brown = lattice defect, green = radiation. Diamonds do have their uses. Their lattice shape makes them one of the hardest materials available on Earth, and they are also great superconductors. Prior to the 1800's, diamonds were extremely rare. The only known small mines were found in India and Brazil. The entire global stash of diamonds was estimated to be only a few pounds, and therefore only the wealthiest of people could afford them. In 1870, the diamond market was devastated by the discovery of massive mines in South Africa; such as large mass of diamonds were suddenly available, causing a crash in the value. By 1888, several mining companies came together under one name: The De Beers Mining Company." By 1902, De Beers owned 90% of diamond mines and production. This monopoly on the market allowed for De Beers to create artificial rarity.
However, this was not enough. Despite the "common knowledge" that engagement rings (particularly DIAMOND engagement rings) are a tradition from antiquity, this "tradition" only began less than a century ago. In the early 1900's there was still not a market for diamonds, because no one saw the worth in the stone. De Beers needed to recreate the market. Their strategy was beyond amazing. Their goal was to push the notion that a diamond = love. This came with some difficulty, because men and women at the time were very preoccupied with social status; if a poor couple can have a diamond ring, a rich couple won't want one. So, instead of simply stating "A diamond ring shows you truly love your woman," De Beers pushed with "The largest, most perfect diamond, shows the quality of your love for your woman." By playing with a man's egos, and pushing a woman's need to show off to her friends, De Beers created their market within record time.
After diamond jewellery became more popular over time, De Beers was able to further restrict diamonds to their seller and increase the prices. This is the reason why, when you try to resell diamond jewellery, it's aftermarket value is usually less than 50% of the purchased price – because as I stated before, diamonds are worthless.
De Beers' monopoly on diamonds has receded recently with the discovery of more massive diamond mines in Canada and other countries, though this hasn't reduced the prices. We've posted about this in more detail, which you can read about here: http://on.fb.me/1E3a4IU
De Beers, as greedy and evil as they sound, is extremely impressive in their ability to build an amazing empire all out of a worthless shiny rock.
Humorous video explaining all this (probably in a more understandable way):https://www.youtube.com/watch?v=N5kWu1ifBGU
~Rosie
Image: http://dailym.ai/1QEnQuD
References: http://huff.to/1zWTVtx
_](https://www.facebook.com/TheEarthStory/photos/a.352867368107647/873670669360645/?type=1&theater#)
The Blue Moon Diamond
Named because such exceptional stones are only found once in a blue moon, the stone displays a very deep shade of boron induced azure that was graded by the Gemological Institute of America as Fancy Vivid blue (without the usual grey colour modifier), and internally flawless. It was mined in one of the oldest mines in the world in January 2014, the Cullinan mine in South Africa, that has traditionally produced some large and beautiful stones, including the whoppers from the biggest stone ever that grace the British crown jewels. It is famed for blue stones, which represent a mere 0.1% of production.
De Beers sold the mine on, and the recovery methods were changed to allow more large stones to pass through the grinding mill. Like many blue stones, it glows phosphorescently in UV light (continues glowing after the exciting light is switched off) a deep orangey red for an exceptional 20 seconds (see our past post on glowing diamonds for an explanation at http://on.fb.me/1GPmnMy ) attesting to the depth and purity of the colour.
The rough stone weighed 29.62 carats, and the resulting cushion cut gem 12.03 carats, measuring 15.57x13.47x7.55mm.
Loz
Image credit: Cora Diamonds.
Diamond mining in Brazil
The diamond mines in Brazil are quite interesting. Diamonds are carried to Earth’s surface in a type of volcanic eruption never seen by humans called a kimberlite. These eruptions form deep in Earth’s mantle and carry crystals, including diamonds, up from several hundred kilometers below the Earth’s surface.
Those eruptions create vertical pipes when they reach the surface. To mine diamonds from these pipes cheaply, the best technique usually is to dig almost straight down, limiting the amount of extra weight moved out of the way leading to incredibly deep holes in the ground like the Mir mine (http://tmblr.co/Zyv2Js1VUXqS4).
The mines in Brazil are still finding diamonds that came up in kimberlite pipes but the eruptions took place oover a hundred million years ago, around the time when South America and Africa rifted apart. Since then, an enormous, tropical rainforest developed in that area, burying the kimberlite pipes and even eroding them.
Instead of looking like deep pits, the mines in Brazil look like this. The diamonds from these pipes eroded and washed down stream. The high hardness of diamonds makes them extremely resistant to weathering, keeping them in tact as water carries them down stream. The diamonds then wind up deposited in river sediments, where the mines find them today.
Some of the black "carbonado" diamonds we covered in this post are found in mines like this:http://tmblr.co/Zyv2Js1bBbuRy.
-JBB
Black diamonds, from outer space?
When Brazillian garempeiros (artisanal miners) first came across these stones in the alluvial deposits near Diamantina during the mid 18th century CE, they named them carbonado (meaning burnt). It is a rare form of diamond, previously relegated to industrial use as drill bits and the like. Ranging from grey to opaque black, they are polycrystalline porous aggregates that include graphite patches and amorphous carbon which give them their colour. Most diamonds are single or twinned crystals, so in this respect they are unique. In the late 90's they started to wax in popularity as gems in their own right, and are now a standard component of the jewellery designer's arsenal. They have only been found in two places so far, both alluvial deposits; the aforementioned Brazilian source and the Central African Republic. Neither area has been associated with a source kimberlite, the lava that froths up from the mantle bringing diamonds up with it, so their geological origin remains something of a mystery, though their formation has been dated using uranium/lead isotope ratios to around 3 billion years ago. Even more unusual, none of the usual mantle inclusions such as olivine, pyrope garnet and perovskite have ever been found in one, though some have had crustal inclusions within pore spaces (not necessarily an indication of where they formed). They have never been found in conventional mines producing mantle sourced stones.
Several theories are contending in the arena as to how these enigmatic diamonds formed. One is by the metamorphosis of organic carbon carried down in the sediment atop subducting slabs in the high pressures that appear as they slide into the mantle. Another is shock metamorphism by meteorite impacts, though no obvious craters exist (barring a magnetic anomaly in Africa), and high pressure mineral inclusions are also absent. A third is radiation formation due to spontaneous fission in the Earth when there was alot more undecayed Uranium and Thorium around, but the Oklo natural nuclear reactors found in Gabon (seehttp://on.fb.me/1C8kcTL) have no diamonds nearby. The last is formation in a supernova when a nearby star exploded or in space during an asteroid impact and then carried to Earth by an asteroid that impacted over the areas where they are now found while they were juxtaposed.
A paper some years back uncovered a tantalising clue that may point to an extraterrestrial origin when the team found that they were enriched in hydrogen, very rare on Earth as all the free atoms of this light gas have drifted out of the atmosphere into space, which is enriched in it. They also have light carbon isotopes, which some have suggested also implies an origin in space, and a mineral called osbornite, so far only found in meteorites, has turned up as an occasional inclusion. See the meteorite studies link below for a complete argument in favour of this intriguing and controversial theory.
They are hard to cut and polish, since they are polycrystalline and each crystal is in a different orientation, The only way to cut them is using another diamond, pointing the hard direction of the cutiing piece onto the soft one of the stone being faceted (yes, some minerals like diamond and kyanite have differential hardness in different directions). Due to their extra toughness induced by their microcrystalline nature, carbonados are required for the most extreme industrial applications. Under the microscope, they contain networks of cracks and black planes and inclusions embedded in transparent gem material. There are fakes around, made by heating cracked diamonds in air to induce graphitisation.
The beautiful Mughal cut stone featured in the photo is the Spirit of De Grisogono black, weighing in at 312.24 carats, the world's 5th largest cut stone. It is named after the jewellery company that pioneered the renewed popularity of these beautiful rocks and was found in Africa. The next largest famous black is the Orloff, at a mere 67 carats.
Loz
Image credit: De Grisogono http://www.meteoritestudies.com/protected_CARBONAD.HTM http://www.geologyin.com/2014/11/geologists-discover-origin-of-earths.html http://www.nsf.gov/news/news_summ.jsp?cntn_id=108270 http://gems-world.com/en/43-carbonado/ http://famousdiamonds.tripod.com/spiritofdegrisogonodiamond.html https://www.gia.edu/gems-gemology/summer-2017-carbonado-diamond
I think there is a flower inside this Crown Jubilee®👑🌷🌷
crownjubileediamond
crownjubileediamond#🌷 #flower
Does De Beers really control the diamond price?
Every time I post on the gemmy form of carbon, some commentators state that the value of diamonds and the entire distribution market for them is controlled by one company. While the latter might have been true until the late 1980's, this is not the case today, and I feel it's time for a bit of a plunge into the history of the diamond trade. As for the former, it's a pipedream. Like other wonders of nature, gem diamonds are rare, as are rubies and sapphires, even though corundum is fairly plentiful in non gem qualities. Before the discoveries in South Africa late in the 19th century, gem diamonds only came from two main sources (with a third minor one in Borneo): The traditional mines around Golconda in southern India (mined since time immemorial, and found in antique Roman rings and medieval jewellery) and the 'recent' discoveries made by the Portuguese in Brazil in the 1600's. At first the new discoveries were a minor influence, but as more kimberlite pipes and placer deposits (reworked deposits from eroded pipes) were found throughout southern Africa, the supply increased and the quality grading grew ever more fanciful (rising to AAAAAA for diamonds of the 'purest water').
De Beers formed as the various African mines (previously divided into individual claims) were gradually consolidated by a cast of unusual characters, some with insane imperial ambitions (such as Cecil Rhodes...as in Rhodes scholarships and Rhodesia) and others eccentrics who were in it for the game and the money (such as Barney Barnato, who started off in the London East End rag trade and was a born showman).
De Beers developed into the biggest centre of expertise in diamonds, their origins, geology, and mining in the world, with an integrated vertical structure that went from mine to gem cutter. This included prospecting, assessing (with a strict grading system), extracting (in the complex engineering environment of deep carrot shaped pipes), separating the wheat from the chaff and moving the produce down the distribution chain via its sightholders (who were chosen on the basis of being able to come up with enough money 10 times a year to make it worth De Beer's while selling to them). These then passed on down the chain the rough that they didn't cut themselves.
De Beers first made synthetic stones and stand at the forefront of detection methods used in gem labs today. They also pioneered research into treatments, and supported the GIA cut diamond grading system when it was introduced (with the best colour as D rather than AAAAAA). When you buy a certified stone, it is backed up by their technology, and their expertise has helped develop the systems used, giving confidence to buyers wolrdwide.
As further discoveries were made, its expertise allowed it to take a part in or be invited into many concessions worldwide. Everyone thought that they would get best value added that way. Even the Communist Soviets (who had made their own discoveries in Siberia and the far north) joined the De Beers distribution system for most of the cold war. De Beers marketed diamonds worldwide, but not in the sense most people seem to believe. Their supply monopoly was never perfect, many sources remained outside their control, and their buyers were stationed worldwide hoovering up as much production as they could, but never close to all of it.
The new African sources allowed gems to be accessible to the masses in a way never before possible in history. Thus the tradition of the engagement ring spread down through the middle classes along with slogans 'is she worth a month's salary', a social custom that the clever marketing spread worldwide, including new places like China and Japan. In a similar manner, the development of heat treatment for corundums by the Thais in the 1980's made rubies and sapphires accessible outside the circle of the super rich for the first time. So yes, like any good company, they strove to grow demand for their product, with a high degree of commercial success. They based this success on mankind's eternal love of bright shiny crystals, whether coloured or clear, that many of you presumably share, (or the pretty crystals I post wouldn't get any likes).
And then came Argyle in the early 80's, the biggest diamond mine on Earth (in the Kimberleys of West Australia) and the main source of the extremely rare pink, purple and red stones. For several decades its production was the highest in the world by far, at 10 million+ carats yearly. Unfortunately most of their production was yellow or brown, then viewed as industrial quality by the DB system.
After many arguments about how to market them, Rio Tinto pulled out of the system and started its own campaign, revealing their stones to be beautiful (and they are) 'champagne' and 'cognac' diamonds. They built direct links with the growing cutting industry in India, whose low labour costs allowed their small stones to be faceted in bulk, and started their own distribution line. The Russians followed suit, and ALROSA (the state diamond corporation) began their own direct auctions and sales in Ramat Gan (Israel) and Antwerp.
As the system was already beginning to fragment, a maverick Canadian geologist (whose extraordinary story I have told elsewhere at https://tmblr.co/Zyv2Js246Z0Pm) single handedly discovered a game changer that would mostly remain outside the existing system: Ekati, which was followed by many more finds in the Canadian Arctic (that DB and others had explored fruitlessly in the 20th century). The gems here are high quality, and without some of the unfortunate associated politics of African stones. The Canadians have developed a mine to finger tracing system, and marketed their diamonds very well.
Other countries who saw this also wanted to maximise the value received for their stones, and began to demand renegotiations or award concessions to smaller independent companies, where the balance of power in the contract would be more to their favour. DB had mixed stones from all over into boxes of varied qualities, claiming the money they earned was in the tweezer used for sorting, that theoretically allowed the manufacturers to specialise in the goods they could cut for highest profit. Now parcels with distinct provenances are common and each country (with the exception of Namibia and Botswana which remain the linchpins of what remains of the DB system) or mine markets its own goods.
The 'cartel', faced with the loss of its monopoly (always relative remember, Mobutu's fief of Zaire for example sold plenty on the side) and with majority rule in its South African home finally realised, proceeded to restructure both its holdings and its system. They gradually divested the old mines in South Africa to smaller companies, exchanged cross shareholdings with its main sources (Botswana and Namibia), left its London HQ and sorting operation for Gaborone and reinvented itself as a 'supplier of choice' with its sightholders. They also started to market high end cut gems and jewellery in their own chain of stores worldwide.
In further complex manoeuvres, it took itself private as part of a restructuring of the Anglo American gold company, which enjoyed a cross shareholdings with DB and the Oppenheimer family. Tracing what all this manoeuvring means is still tricky, as it is too recent to really evaluate the consequences.
The main current problem in the diamond trade is in part a consequence of this strategy, since the prices of rough are ever increasing and those of polished goods remain more or less level. Many smaller cutters are going out of business, and the number of middlemen in the trade is going down, as both the mining companies and nations work to realise the maximum value possible for their own production ( by for example keeping a share in an important stone when sold to the cutter) and start new cutting centres to maximise locally added value (and jobs). Inevitably this means taking the extra money from elsewhere in the distribution chain, since the price of polished goods remains stable or down.
As for the second allegation, that diamonds are as common as peanuts, I'll ask you all, when did you find one last in your back garden? They may be less rare than top end unheated rubies, tsavorites and red beryl, but mining production still sees a carat per million tons of shlep as pretty good. That's alot of earth to shift for a carat, especially if you bear in mind that most production still falls into the industrial category, champagne and cognac notwithstanding. And as for fancy coloured diamonds like the Hope blue, they are super rare.
As ever in these matters, things are more complex than anyone attempting a simplification (this post included) can describe for a public. The gem trade has always been secretive, about sources and clients, sales and purchases, prices paid and charged. Add in the need for operational security with small high value goods subject to robbery and the murky end of international politics, then you have a situation in which, as ever in interesting historical matters: those who truly know remain silent, those who speak, speculate.....
Loz
Image credit: De Beers
Diamond octahedron
This spectacular single crystal was recently mined at the Rio Tinto Company’s Argyle Diamond mine in Western Australia. That mine is most famous for producing many of the large pink diamonds available on the gemstone market in recent decades (see:https://tmblr.co/Zyv2Js2hbwbUY). This one, holding an excellently formed octahedral shape, was measured at over 28 carats. Look closely and you can maybe even see a few etching marks reflecting the internal crystal structure appearing on the faces. The specimen will be shipped to market in Europe before it is likely cut into whatever its final state will be.
The Rio Tinto mine is slated for closure in 2020, so this find may wind up being one of, if not the, last large stone pulled from this mine.
-JBB
Image credit: Rio Tinto mining References: https://ab.co/2W4eFvQ https://www.naturallycolored.com/diamond-education/argyle-diamond-mine
The Mind Stone
Intense yellow colors found in rare diamonds are some of the most valuable gemstones around. This stone, the Tiffany Yellow Diamond, was originally found in a diamond deposit in South Africa in the 19th century, and was eventually purchased by the Tiffany company. When it was loaned to the Smithsonian Museum of Natural History in 2007, it became the largest diamond on display in the U.S. – it is 3x the size of the famous hope diamond.
This necklace has only been worn 3 times; by Mrs. Sheldon Whitehouse in 1957 to the Tiffany Ball, by Audrey Hepburn in 1961 for publicity photographs for “Breakfast at Tiffany’s”, and at the 2019 Academy Awards by Lady Gaga.
Diamonds, famously, are nearly pure carbon. Yellow diamonds get their color from a bit of nitrogen substituted in place for the carbon. Carbon atoms in diamond typically share 4 electrons, but nitrogen has 5 electrons rather than the typical 4 for carbon. This extra electron in nitrogen can be excited by blue-colored visible light into a conduction band, causing nitrogen-bearing diamonds to absorb blue light and appear yellow. This color is thus the same mechanism that produced the color in realgar – a band gap color, with electrons able to jump from one atom to another if they’re given just a little push by visible light.
-JBB
Image credit: https://flic.kr/p/LKUTsf
References: http://famousdiamonds.tripod.com/tiffanyyellowdiamond.html https://www.wmagazine.com/story/oscars-2019-lady-gaga-tiffany-diamond-necklace-audrey-hepburn https://4cs.gia.edu/en-us/blog/yearning-yellow-diamonds/ https://www.diamonds.pro/education/canary-yellow/ http://www.webexhibits.org/causesofcolor/11A0.html
The Argyle Pink Jubilee
The most consistent source of pink, purple and the very rare red diamonds is the Argyle mine in the remote desert wastes of Western Australia (seehttps://www.facebook.com/TheEarthStory/posts/516555285072187), and the annual tenders in Perth are one of the fixtures of the high end jewellery market since these special stones are usually cut in house so as to maximise the added value. There are only ever a few stones for sale over a carat, maybe half a dozen yearly. The largest rough pink ever found there (in 26 years ofoperation) is this slightly etched distorted octahedron, which weighed in at a puny 12.76 carats (2.552 grams). The colour is a pale but powerful rose, similar to the Williamson Pink, found in Tanzania and gifted to the Queen of England on theoccasion of her wedding by the mine owner. Unlike most of the mine's production, this stone ended up being donated to the Melbourne museum (where it on permanent display) after being the expected star of the show at an invitation only tender in 2012. Luckily for the world, when they started cutting it they found a knot, an internal line of stress and incipient cleavage reflecting the stone's exciting geological history during the process of formation or eruption from the mantle in the lamproite pipe that brought it to the surface (these knots are known in the trade as a gletz). When the saw or scaithe (the round polishing disc) encounter these knots, the usual result is that the stone promptly explodes into shards as the internal strain is released.
The preshaping removed 4 carats (it is common to lose 40-80% of a rough diamond during cutting) before it was donated to the museum, but pieces like this almost never end up in such places in the rough. Rich patrons sometimes donate cut stones, such as the Hope at the Smithsonian, but commercial companies tend to sell all their rough. While they could have cut several smaller stones out of the rough, it was decided to donate it, since it had been the largest Argyle crystal ever found. Since the museum had a long standing relationship with Rio Tinto, they got the lucky prize. Next time I'm over that way I guess I'll drop round and visit it.
Loz
Image credit: BBC/Getty http://roskingemnewsreport.com/The%20Argyle%20Pink%20Jubilee/ http://roskingemnewsreport.com/the-2012-argyle-pink-diamonds-tender/ http://www.smh.com.au/executive-style/luxury/precious-pink-sparkler-lights-up-museum-20120712-21yyz.html http://www.bbc.co.uk/news/world-asia-17108778
Myrni Mine
The Myrni mine (also called the Mir mine) is an inactive diamond mine that began production in 1957 and ceased activity as an open pit mine in 2004, although mining has since moved underground. As with most diamond mines, the rocks being dug up were kimberlites – the result of violent volcanic eruptions that start deep beneath Earth’s crust and carry intact pieces of the mantle, including diamonds, rapidly up to the surface.
Kimberlite eruptions produce vertical pipes that break through the Earth’s crust, so the best way to mine them is to dig straight down. The more excess rock moved out of the way, the more expensive the mine is to operate, so to get at the ore, the miners dug as close to straight down as possible, leaving only tiny ledges to prevent rockfalls. Near the end of its operation, it took nearly 2 hours for a vehicle to drive from the surface to the bottom.
The mine is over 500 meters deep, making it one of the 5 deepest man-made holes in the ground and 2nd largest by volume. Whether it’s true I’m not sure, but there is a long-running story that this site was declared a “no-fly zone” for helicopters due to downdrafts in the pit creating unsafe flying conditions.
-JBB
Image credit: https://www.flickr.com/photos/jeande/2730864493
How wet is the Earth?
It seems like it should be easy to figure out the amount of water on the Earth, right? Just sum up the volume of the oceans and you’re 99% done. In fact, you might have seen graphs like this showing how moons like Europa have lots more water than the Earth.
That would seem to work except there’s a problem; minerals. Many minerals can hold water in their structures. Some of these minerals occur at the Earth’s surface; clay minerals, for example, hold large amounts of water that can be released if the minerals are heated. The same is true for minerals that sit deeper down.
The volume of the Earth’s mantle is enormous compared to the volume of the oceans; the oceans are about 0.1 of the volume of the mantle. The mantle is made up mostly of minerals like olivine which don’t take nearly as much water up as clays, but instead those minerals do something different. Tiny amounts of water are able to dissolve in many minerals including those of the mantle. Under some conditions, minerals like olivine can dissolve about 0.1% water in them – almost enough that you could hide a full ocean’s worth of water in Earth’s mantle.
But olivine isn’t the only story. As pressures increase in the Earth, the structures of minerals change. Deep in the Earth, about 500 kilometers below your feet, the structure of olivine changes to a different mineral called Ringwoodite (named after a petrologist named Ringwood). Scientists have made ringwoodite in the lab and found, remarkably, that it can hold over 1% water.
Ringwoodite only makes up a thin slice of the mantle, but if there was enough water available, that one mineral could hold an extra ocean’s volume of water, or more, within its structure.
The trouble is, prior to a few years ago, we weren’t sure that much water was there. Ringwoodite can also be dry – if the Earth’s mantle just doesn’t have much water in it, ringwoodite will still happily exist with no water in its structure.
This leads me to research published in the journal Nature by scientists from the University of Alberta and Goethe University. Ringwoodite occasionally comes to the Earth’s surface trapped inside the structures of diamonds that grow deep in the mantle. When those diamonds come up in volcanic eruptions called “Kimberlites”, they carry the ringwoodite with them and store it until scientists come along.
This group of scientists found interesting ringwoodite grains in diamonds from Brazil, took them into the laboratory, and found that they had >1 % water in them. These ringwoodites were soaked!
This is the first real strong evidence that the Earth’s mantle could be hiding a whole lot more water than we think. These grains might only be sampling one very wet spot in the mantle, but they definitely show there are areas in the mantle that are very, very wet. The Earth’s real water bubble is a whole lot bigger than the one in this image. Maybe many times bigger.
This result suggests there is a whole lot more water than this bubble buried deep within the minerals of the Earth’s mantle. Ringwoodite isn’t the only mineral that can hold lots of water in it, so if there are areas where it is soaked, other minerals in the mantle could be soaked too. If that’s the case, it will be a very important result for understanding how the Earth was built, how much water the planet formed with, and maybe even when life was first able to form on Earth.
-JBB Image credit: NASA/APODhttp://apod.nasa.gov/apod/ap120524.html Read the paper:http://www.nature.com/nature/journal/v507/n7491/full/nature13080.html
Blue diamonds start in subduction zones
Diamond macle
In a recent post (see http://on.fb.me/19XRzNF) we discussed the idea of twinned crystals, illustrated with three beautiful pyrite crystals. Macles (from an old heraldic word for lozenge) are a more complex form of twinning, in this case representing two octahedral crystals that have grown together, ending up with this triangular slab shape.
They are very hard to cut, since the twin plane that separated the crystals within the gem marks a change in orientation, and hence a change in hardness known to diamantaires as a knot. Diamonds can only be cut because they have different hardness in different direction, so the hard direction of one diamond is used to cut the softer one of another. Working with macles is a subtle and risky business, since accumulated strain from past tectonic pressures within the ston can cause it to explode when the knot is reached.
Jewellers have started using these diamonds in the rough as the centre tone of unique design pieces, and I much prefer this to a faceted brilliant.
The triangles on the surface of the crystal are known as trigons, and very common in diamond. They reveal the crystal structure, being formed as the crystal gets partially dissolved away during its rise to the surface in its carrier kimberlitic magma. Cheats have even engraved them on imitations made of say transparent synthetic corundum to make their fakes look real (remember that the number of synthetics you see in the trade is inversely proportional to the distance from the mining area, I have seen some very cunning ones such as pouring green lass into a mould made with an emerald crystal and then sticking gangue minerals on over the result).
Loz
Specimen from South Africa, 1.5 x 1.5 x 0.4 cm, 9.94 carats weight. Image credit: Rob Lavinsky/iRocks.com
