diamond jewelry india

>> okay, thank youfor the introduction. yes, i've been herefor quite a while, and this presentation is -- i just want to give thanksto a number of people, especially research students andpost-docs and my sort of mentor in a way, judith milledgewho, amassed a collection of diamonds, which are presentat ucl, which enables us to study natural diamonds. and judith milledgewas, herself,

has an excellentpedigree, if you like, from kathleen lonsdale. and the diamond has a longhistory of evolvement at ucl. so kathleen lonsdalehas many accolades: first female professor at ucl, and first female memberof the royal society. and judith milledge started workhere on diamonds at around 1950. and the slide isjust to show the sort of diamonds we'remore interested in,

not the shiny ones on the left. we're much more interested indiamonds with inclusions in, so you can see the red garnetinclusion in the diamond itself. and that usually meansthat the diamonds we deal with are less spectacular,though the same material. and if they're grubby and havegot inclusions in or dark, we do quite wellfrom the pieces, which the diamondindustry discards. so we look at theinclusion-rich parts

of diamonds, in particular. i've been involved withlooking at the origin of carbon-rich magmas andhow they deliver materials from the earth's mantleto the crust through time. and this has led meto perform experiments to see how thosesystems operate, both the crystals and the melts. and it seemed natural,therefore, to look at the carbon cyclecoming from the deep earth

to the earth's surface, and so diamond is alogical material to pursue. so my background is inhigh-pressure experiments and looking at minerals, whichdo come from high pressures. so by way of introduction,it wasn't until the 1950s that a diamond was grownand confirmed to be grown under high pressure, hightemperature conditions, although there weresome earlier experiments in the previous century, whichreported to have made diamonds

by high pressure andhigh temperature. and there were some fascinatingstories attached to whether or not those hannaydiamonds were legitimate or they were salted asbeing natural diamonds put into the experiments to make itlook as if they had been created at high pressure andhigh temperature. that debate stillisn't quite resolved, but part of the story isbased around the experiments of high pressure and hightemperature are inherently

very dangerous. and hannay, himself, didn't actually conduct theexperiments, he had a manservant or two, a technician, to actually performthe experiments, and they were life-threateningexperiments because the equipment usedto explode quite regularly. and after some time, i thinkit was more than a year or so, it became clear thatgoing to higher pressure

and higher temperaturewas even more dangerous. so at that time miraculouslythey produced diamonds, and it may be the case thatthey were actually salted by the people doing theexperiments in order to preserve themselves. so this is one possibleexplanation for some of the diamonds being attributed to hannay have unmistakablecharacteristics of natural diamonds ratherthan synthetic diamonds.

so about since the 1950s, a growth of a diamond wasperformed at high pressure and high temperatureusing metals as the melt, a melt catalyst at very highpressure and temperature on the basis thatmeteorites were seen to have high nickel metal inand they also had diamonds. and so the same method was used to produce diamondscommercially effectively, and has been since that time.

there are other methodsof producing diamonds, including explosive detonation. this is based around,or developed by a gentleman calledpaul decarli. i'll put a pictureof him later on, and his particularmethod was also dangerous, and generally led topeople losing their hearing who i can see, and thepeople actually have evolved in that part.

and then more recently, we havehad chemical vapor deposition, which is the directdepositioning of diamond out of its stability field. so this is the onlymethod on here which isn't high pressureand high temperature. it [inaudible] high temperature,but at very low pressure of an organic gas, andwe'll see a little bit of that later on, too. all the methods whichyou can make diamond

with produce what i wouldcall synthetic diamonds, and they differ from naturaldiamonds in some ways. not in their major materialproperty, but they do differ in the way that the nitrogenimpurities, in particular, are accommodated inthe diamond lattice. and also in terms of the, they don't have the mineralinclusions, which you can see in natural diamonds which cansometimes be very colorful, red and green colors,for example.

so the outline ofthis talk is going to cover a very widespectrum of ages, which is practicallythe age of everything and the origin of everything. so starting off withthe big bang. and you'll see this slidepop up from time to time, and red color zones go throughso you can get an indication of the pace of the lecture, so you can see what'scoming as well.

and we start off with the originof the diamond in the universe. one would have to say that carbon is a very abundantelement in the universe, in our solar system,in particular. fourth abundance in howeveryou measure it, fourth in terms of abundance of elementsin the periodic table. but, and if you lookat meteoritic material, which is our samples of oldthings going back as far as we can in time thatwe can get our hands on,

the vast majority of allmeteorites contain diamond in one form or another,usually nanodiamond, and so it's incredibly finegrained, dust-grained size. so i like this slideas a starting point because it shows all matterand all time in one slide. and i actually triedto draw this myself, but i could never come up withthe concept until somebody at nasa drew it for me; infact, i borrowed their slide. the wilkinson microwaveanisotropy probe is looking

backwards towards thefurthest distance in time, and it's been involved in makingsome headlines quite recently. and so you start off on theleft-hand side with the origin of everything, which youmight call the big bang, and you might decidethat's more than one event or a single eventdepending on what you make of the horizon program,for example. and you can count thegirdles going left to right in one billion year time steps.

so, if you start at thisend, this is current day, and that is 13.7 billion yearsago, the origin of everything. so if we count back 4.6billion years, around this point in time is the formationof our solar system. and this is an example ofwhat we see if you are able to image nanodiamonds in chondritic meteorites,for example. so this gold bar on the bottomleft-hand part here is five by one nanometers,and you can pick

up some crystalline structures. the bright spots in hereeffectively are locations are diamond-like structures in whatcan be retrieved as nanodiamond. the open universityhave become experts at collecting nanodiamondsfrom meteorites. it took them, i think, more than 10 years before they couldactually analyze them properly. and i was told, i don'tthink totally flippantly, but they realized the first nineyears they had been filtering

everything and then eventuallythrowing the last part down in the sink. so it was very, youcouldn't actually realize where the nanodiamondwas residing when you dissolveeverything else into a sample, so basically you justuse acid digestion. but now they're able to subdivide nanodiamondsinto different types. so we start off withearly formation of dust,

and we're not quitesure how that happens, but diamond is associatedwith the earliest products that we have record for. and on the right-hand side,here is a phase diagram, so pressure going across to theright, and temperature going up vertically in thousandsof degrees, and pressure across here in gigapascals,10, 20 gigapascals. if you went further to theright, the core mantle boundary, which is sort of halfwayinto the earth if you like,

would be at 135 gigapascalspressure, just to give you idea. and i've put some other, well,actually another slide, sorry. so this shows the stabilityfield for diamonds, here labeled as cubic diamonds, and thengraphite on the left-hand side, so the conversion from graphite to diamond follows this nearlystraight line which is inclined as a function ofpressure and temperature, and was first derived bya scientist called bundy. and so this line here is thereaction or stability curve

between graphite and diamond. materials which are anyform of carbon should be, should crystallize as diamondto the right of that line and form graphite tothe left of that line. if you then know that thegeotherm in the earth, which is the increase intemperature with pressure as you go down in theearth follows this curve, you'll realize thatthe vast majority of that sits in thediamond field.

so you cannot make graphitestable inside the earth because it's too high a pressurefor the given temperature. the only part of this diagram which is possibly wrong isthis curve here between diamond and liquid, whichgives the impression that if you go towardsthe core mantle boundary, carbon-based materials likediamond will become a liquid in the core mantle boundary. that curve actuallygoes the other way,

so that as you go towards the -- it is now thought to go theother way theoretically, so that diamond actuallybecomes more stable as you go to the right in this diagramfor any temperature rather than getting less stable. and what this diagrameffectively shows is, and what we know, is that thediamond itself would be stable to pressures more than twicethe pressure and temperature at the center of the earth,

which means that once youeffectively have made diamond, it's very difficultto get rid of it. so even a planetary,interplanetary collision between two planets orbodies the size of the earth, you might cause all thesilicate material in the outside to remelt, but you could notactually get rid of the diamond that was there previously. so that's my basis for understandingdiamond and its stability.

this diagram shows a lot ofinformation; you can look at it at several different levels. here's an image ofthe diamond structure. you'll see that cropup on another slide. on the bottom, you'll seea familiar form of diamond. of course, you'd all liketo have that one that size. and then on the bottomright-hand side we've got just an illustration showinga similar -- actually, these aresmaller ones --

similar diamonds that are justshowing their array of colors, so this is just theirphysical characteristics, their optical properties. the two blue diamondshere have been sectioned, which in itself is challengingbecause you have to go to some lengths to polishdiamond to flat face, and they are illuminatedunder cathode luminescence, and this particulartechnique is very powerful for showing texturesinside diamond, which,

in ordinary light, wouldbe completely transparent or not visible. and it's a long, destructivetechnique, so you can apply it to the exterior stones andstill see these textures, which look more or lesslike growth rings in a tree, and that is more or lesshow they're interpreted. so these concentric zoneshere echo the shapes or the crystal growthfaces of diamond, which is showing an octahedralsymmetry here in the center,

and then the exterior ofthe diamond is more rounded. but you'll also notice thedifferent shades of blue, there are some highspots which are brighter, and then the shades of bluethemselves generally correspond to different intensitiesor different contents of nitrogen in the diamond. so diamonds are actually closeto being a pure material, but they contain naturallynitrogen within them, as well. and they're classified intotwo main types of material.

they're classified into diamondwith measurable nitrogen, which means more thaneffectively about 80 to 100 parts per million,and that goes up to about two to 3,000 parts permillion, occasionally more. or they're classifiedas diamonds without detectable nitrogen, which actually doesn't mean theyhaven't got any, it just means that we can't detect it. so those are diamonds with sub80 parts per million nitrogen.

and so we can startstraight away by saying that diamond is almostall carbon, but there is a little bit ofother material in it, as well. and some of thesecolors are generated by occasional impurities, orstrain in other features too, but one or two of thecolors can be generated by very small amountsof other impurities. the image on the left hereis a black and white image of a cathode luminescencegenerated view,

so here we're seeing a cubicshape, more of a diamond. and the bottom left-handimage here is a very, very strange blackdiamond called carbonado, which we'll return tobriefly at the end, which has got a melted surfaceto all intents and purposes and an unknown origin. both the carbon and the nitrogen in diamond have specificisotopic characteristics. you know, both of thoseelements have got isotopes,

carbon's got stable andradiogenic, but if you just look at the stable isotopes,on here is the 13 to 12 carbon isotope ratio fordiamond, or for any material. this is comparing the locus ofpoints for enstatite chondrites, in fact, with somemantle diamonds. the mantle diamonds occupythe histogram blocky sort of tower shapes, and thedots encompass the range, which is known from,as you can see, hundreds of enstatitechondrite meteorites,

which have now been measured. and you can do thesame for nitrogen. this is the 14, 15, 15,14 nitrogen isotopic ratio to some other material, so we get this strangeper mil notation. and the terrestrialvalue for nitrogen to mantle lies a little bit tothe right, i think you can see that even for the diamond,compared with the peak for chondritic meteorites.

so they don't quite match up,but they're not a long way off. so to first approximation,you could actually say that diamonds made fromcarbon and nitrogen, which are both moreor less identical to what you can findin meteorites. and the last, this last part toshow you the nitrogen story is that because diamondsare transparent, you can use spectroscopyvery efficiently to look at vibrations in thelattice of the diamond

and understand what othercomponents there are in diamond apartfrom just carbon. and if we use infraredspectroscopy, you can look in this region -- these peakshere are for different types of nitrogen in thediamond structure. this is a diamond response,self-absorption, if you like, and these peaks are very rarelyseen, but they're put on here to indicate wherethey would occur. these are two peaksfor hydrogen or water

in the diamond structure,too, which you can also find. not common, but definitelyoccurs in some diamonds. so we can use these features. the shapes of these peaks and their widths caneither be totally absent if you've got a type, a diamondwhich has no nitrogen in it at all, then these peaks willbe simply completely absent, and obviously, the heightof the peak increases with the proportion ofnitrogen that's in the diamond.

so you can use those peaks to tell you not only howmuch nitrogen is there, but also what state it's ininside the diamond structure. if we turn to some syntheticdiamonds, the little code down here is to show we'reproducing exactly the same material. it has the same hardness, the same physicalproperties as natural diamond. but when you look at them,

they have often gota yellowish color. this is one particulartype of synthetic diamond. the diamond is made inassociation with metal melts. they could even have enoughiron or nickel in them that you can attractthem with a magnet, so you can be quite sure they'renot normal, natural diamond. the yellowish coloris dominant, as well. and we spend our time,i should say, at ucl, not trying to growdiamonds to sell, you know,

perhaps that mightchange in the future. but we actually just areinterested in the conditions under which they can grow. so for us, normally whatwe start with is more like the image on theright-hand side here. this is a sequenceshowing material, which is first preparedas a flat substrate. it is then introduced insome experimental condition, and what we look forare precipitate growths

on that surface togive us an indication that we've entered the stablephase for precipitation of diamonds, for example,as opposed to whatever was in the starting material;in this case, it was graphite in some mixture. so these are experimentsconducted at pressures of 5 to 10 gigapascals and about 1500degrees centigrade, typically. and you can grow diamondfrom a lot of things and you can grow it very fast.

so in our experiments upto 20 gigapascals pressure, we can produce these sorts oftextures in seconds, in fact, and diamond growth isextraordinarily fast as soon as you get the right conditions. so this gives you alittle bit of a conundrum, because how do we thencompare our very rapid growth in the laboratory with what musttake a very long period of time, perhaps, in natural systems. so here, we are growingdiamond in the laboratory, then,

focusing on that part. and just to recapthe three methods, which i very brieflytouched on at the start, which can grow diamonds. the high pressure, high temperature formis the dominant form, which we think a diamondis grown in nature. there are just some ideason the left here to try and get you thinking about whatthe equivalent in pressure is.

most people are familiar withtemperature, because, you know, that sort of thing you cancount every day, but they're not so familiar with pressure. and pressure is actuallynothing at all extraordinary, it's just a condition you applyto your sample, from my point of view, but yes, it does,you do have to be careful. usually in our situations,unloading is dangerous, loading is dangerous, sohere are some equivalents to think about.

something like 150 kilometersvertical pile of rock sitting on one, you know, area forarea would give you the same equivalent pressure. and we have to containthis, usually in a volume of about one millimetercubed for a few hours. so, in fact, this is actuallyrelatively straightforward to do, focusing yourpressure using the stiletto heel approach. we use an assembly of anglesmade of tungsten carbide,

which is very hard, and thenour experimental material is in the center, it has electricalleads leading in and out. and there are ceramics inhere which act as insulators, but also there is a furnaceinside the whole pressure structure, a tiny furnace insideagain which is your sample, and the pressure is applied by just a very largeuniaxial press on the outside. so that in one form or anotheris how we can grow diamonds in the laboratoryby high pressure,

high temperaturesynthesis, and it replicates to a first order how we thinkdiamond has grown in nature. a lot of syntheticdiamond uses a catalyst which we don't think happensin nature, metals, but, and there are detailsthat are different between the nitrogen isotopes-- the nitrogen bonding, sorry, and the diamond. the other method which imentioned by paul decarli. paul decarli is anelderly gentleman now

who has been involved in a lotof his life with verification of nuclear test bans and lotsof his work was not published because it was, obviously,secret, in the usa. but during that time, heactually did a lot of work on problems of scientificinterest, and his method of producing diamond isvery widely recognized. and you can produce itas a tem image again. the little black and white imagehere is the 10 nanometer scale bar showing a cluster ofnanodiamonds produced by,

either by shock in a --this is a very small diagram of a very large piece ofapparatus which is similar to a battleship gun, simplyfires a projectile at a target. it gives you a shockwavethat way. but paul also used a lot of -- he had massive explosivesranging up to nuclear detonations,let's say, which were able to produce conditions whicharen't going to be copied in a short space of time.

but the detonation methodsimply relies on applying shock in the explosion to graphiteto the direct conversion of graphite to diamond. the difference in thermalconductivity between diamond and graphite means thatyou are limited in size to, of actually what sizeproduct you can make, so you can only makefine material. chemical vapor depositionis a now widely used, certainly laboratory techniqueto grow diamond surfaces.

you can precipitate them onto other material surfaces as coatings, and obviously thecritical interface, the bonding or the nature ofhow they attach, is where a lot of energy goes. but you can also, if you keepprecipitating the diamond from vapor, and there'sa little schematic here which describes itprecipitating as a condensate, like frost on a car windshieldwhere it's not quite the same, there's a lot of muchhigher temperature involved,

and some control of theorganic gas that goes in. but the organic gas containingcarbon is the source of carbon which is deposited as diamond, completely out ofits stability field, so it is a low-pressurephenomenon. you can produce -- here it showssome circular plates of diamond up to a few centimeters across, but only a few millimetersin thickness. and if you keep usingthe same technique,

and actually sometimes it wouldhave to be reground in between to remove defects, but youcan gradually produce larger diamonds, so it is possibleto get, if you like some "flat-ish" shape of syntheticdiamond grown by this method, because you've got a morethree-dimensional shape. and we think there arenatural examples of all three of these ways ofgrowing diamond. so the last part here is justnow to show you some examples of the diamond researchwe've been doing

at university college londonfor the last 10 years or so. yes, the picture ishowed you before of a serious growing diamond inthe presence of hydrous fluids, in fact, and hydrousalkaline fluids, so sodium or potassium rich, oftencarbonate bearing fluids, but certainly with a lotof water in the system. it doesn't mention it here,but the experiments themselves, these are returning to slightlymore dangerous enterprise because, once you havevolatile material, then you have

to be quite careful how youload your sample and heat it or you generate gas,which isn't desirable. so here we're lookingat some, you know, plotting on here the conditionsunder which we were successful in growing diamond and comparingthat with the standard, if you like, graphite diamondcurve, and our objective was to try and see if we couldmove the temperature bar down. so if you look at thetemperature scale, these are growing attemperatures below 1200 degrees,

probably close to about 1,000degrees we still have growth of diamond. as you get to lowertemperatures, even lower than this, if diamondgrows, it then becomes sluggish through kinetics, so youcan't really see it that well. other things we've been looking at are quantifying the opticalbirefringence of diamonds. if you know the thickness of your diamond you'relooking through, it's possible

to interpret directly the storedstrain energy in the diamond and use this to recalculateconditions under which you wouldreturn that to zero strain. and this is kind of likereversing the story for strain around inclusions, whichwe do see in diamonds, to tell us where the diamondshave come from, what pressure and temperature they mayhave originated from. so this is a useful technique. you can use it look atimpurities or damage

in materials, but we'reactually trying to use it to retrace the paths of individual diamondscoming to the surface. this slide is a little bit toobusy, and i apologize for that. so, actually all it's reallysaying is the top line that we're looking atthe isotope behavior of carbon isotopes, inparticular, during the growth of diamond, and how itpartitions between the diamond which is grown and the carbonisotopes of the parent material.

and this was a bit of a surpriseto us, really, that we were able to produce, in effect,that was measurable, because we were thinkingthat actually high pressure and temperature fractionation of stable isotopes wouldbe negligible to zero. so it wasn't with the greatestenthusiasm we started the experiments, but to oursurprise, we were able to find that we can actually invokequite a significant change in stable isotope depositionof diamonds, so it can come

out with a differentstable isotope signature than the startingmaterial, and we're currently in the process ofquantifying that. natural diamonds, perhapsthis line is useful. woops, go back one, sorry. there's only a coupleof more slides to go. natural diamonds do show a rangeof 13 to 12 carbon isotopes, and these have been used toinvoke one origin of quite a lot of diamond as being theresult of diamond formed

from subducted organic carbon. so that if you like, evensome very old diamond appears to have a record of life,which has been converted back to inorganic carbon in the formof the stable isotope signature. now this has been a wildly heldview for the last, probably 15 or 20 years; however, our experiments are nowactually casting doubt on whether this process isreally viable in the light of the fact that we're ableto reproduce the same sort

of isotopic shift withoutany life in our system. so it doesn't reallyrule it out, but it gives an easieralternative in the middle of the mantle, for example, where you wouldn't reallyexpect much life to be existing. diamond anvil cellis just an example. the bottom right-handone, i think, is the very firstdiamond anvil cell. if you put the pointedends of diamonds together,

because diamond is so strong,they've got a very tiny, flat surface, you can generateextraordinarily high pressures, and there are twodiamonds in here. this is simply a cantileverwith a screw device on the end so that the force on here ismagnified onto the diamonds. here all the forces areapplied to the diamonds, and this is currently the way of generating statically thehighest pressure that we can for any material, in fact, ican get more than the pressure

of the center of the earth. the trick, if you want toget temperature, as well, is that you have thenfire a laser through here to supply the heat, but it'san extremely useful method. so this is a use of diamondrather than actually looking at diamonds, themselves. and just to show someimpact diamond here from possibly a meteoriteimpact such as this, actually the source wasn'tknown, but it is possible

to find nanodiamonds andfabrics in nanodiamonds that are very similar to theshocked synthesized diamond. so, you know, weknow this diamond on the left-hand side is madeby shock in the laboratory or with one of those gunsor an explosive event. and we know this nanodiamondhere came from a boundary layer, which is thought to be formed bymeteorite impact, so there seems to be a fairly good tie up thatnatural diamond can include also, impact diamond.

two more slides, i think. we're nearly there. so some of the general questionswe're trying to answer, you know, these are questions wehaven't got an answer for yet, but diamonds are unique in thatbecause of their great age, they have seen a lotof events on the earth. we think some of themhave actually been erupted and subducted and comearound more than once. so that takes two or 300million years for each cycle,

which is quite extraordinary. but we're hoping to usethings like trace noble gases, which are containedwithin some diamonds. most diamonds that come fromthe mantle come from only one or 200 kilometers depth. a few seem to have comefrom maybe five times that, so we're particularlyinterested in those, having sampled very deepparts of the earth's interior. and many of thesequestions are speculative,

but some of them noware more directed so that the last questionon here, how much carbon is in the earth, which we stand areasonable chance of addressing, because we can dosome mass balance with the carbon isotopestory in diamonds. so i think this is thelast illustrative slide. just to show you insome of this carbonado, the black diamond material, wehave delicate forms of nitrides in holes, if you like, in thediamond, which have never been,

these particular minerals havenot been seen on the earth. and there are two or threespecific minerals in this group which are forms of copper silverbearing titanium nitrides. they're not quite the same astitanium nitride, which is known from meteorites, which iscalled osbornite, but they are, in themselves, worthy of morestudy, and that's planned. the group of carbonados,just to show you, not all carbonadoslook the same. so those two materialsare both called carbonado.

one looks like a sinteredpiece of gray road tarmac or something, i don't know, and the other one has got amelted surface on the outside. so actually, carbonadosare not well known. i think i shouldstart with that. and probably what we'relooking at here is a subgroup of carbonado; theseare extremely rare. so this has beenconjectured, these groups of materials have beenconjectured to have come

from supernova events, asbeing extraterrestrial, or from break up, therefore, ofan astroid, and there are lots of arguments you can read whythat may or may not be true, and i've put thecounterargument in here that others think they'reentirely terrestrial. so the jury is out onthose, but that's some of the most interestingmaterials. so finally, in conclusion, i hope i've shown you quite afew different views of diamonds,

and that it's gota lot of potential for study still in the future. some of the major conclusionsi once made is it very hard to destroy. of course, you can react itwith oxygen quite readily; it burns as a ratherexpensive fuel, if you want to go that way. but even in planetarycollisions, therefore, it's very, very difficultto get rid of diamonds,

so there is generallythe prospect that some diamond maybe older than the earth. and because it's so old, it may record significantancient events, such as perhaps theevolution of atmospheres, and we're hoping there is somecombination of noble gases in looking at the nitrogen,there might still be trapped within diamonds some informationrelated to the formation of the earth's atmosphere,for example.

okay, that's it. thank you. [ applause ] >> thank you, a fascinatingtalk there. we do have a few minutes ifanyone has any brief questions. if you do have a question,please wait for one of our roving microphonesto reach you, because this lecture is beingstreamed for the internet, and people on theinternet won't be able

to hear you without a mike. so does anyone have a question? all right, down here in front. there's a microphone behind you. >> thank you. i wondered aboutcolored diamonds. you showed us some. are there other colors, and howwould they achieve those colors? >> in natural diamonds, there'sa fairly restricted range

of colors. pinks are abundant, really. yellows are abundant, brownsand pinks and yellows. blue is rare, and bottlegreen there are two of. so, you know, somecolors you can find. some are exceedingly rare. it's possible tosynthesize diamond, even to about one carat sizenow, and introduce colors which are generally pastelshades, and those pastel shades

of each attracted a salesname associated with it. and so long as syntheticdiamonds are recorded as synthetic diamond,then there's no conflict with the natural diamondbusiness, if you like. but natural diamonds --some of the green ones, you can find coats of diamond which they've got an exteriorsurface which is green, and inside they'recompletely colorless. but the green on theoutside has the effect

of making the whole stone green, and that's usually dueto radiation damage. so it's a bit greenish. there's one in the middle here. >> hi. i wanted to know whetherthere are materials as hard or harder than diamonds, and ifthey have a similar structure. >> good question. a diamond itself has a hardnessof 10 on the hardness scale, but there are someorientations of diamond,

which are slightly harder, sothat, you know, this is one way that you can actually polishdiamond with diamond itself if you know the preferredorientation of your material. so it goes up to about10.1, strictly speaking. there are natural,well, fairly recently, there are some natural materialswhich are harder than diamond, and they are also carbon based. and they've been described, ithink, in some impact materials by a german scientist called[inaudible], well, i'm not sure

if he's german, he'sworking in germany. so i can give youthat information if you want just anatural material. we haven't yet, to my knowledge, synthesized anythingthat's harder than diamond. you can have compositematerial which behaves harder than single crystaldiamond simply because it doesn't have -- you know, natural diamond has acleavage so that commercially,

most diamond which you findis polished on all surfaces but one, one littlesurface is broken, because it's too hard to polish. so that's the risky part of thediamond gem business, really. >> a synthesized diamond isharder than natural diamond? >> sorry? >> a synthesized diamond is -- >> yes, they're identical. yes.

>> any other questions? there is one down there. you said that you thoughtdiamonds might have gone through several cyclesof subduction. are there changesin the properties of these diamonds during thissubduction process in terms of impurities or faults? >> yes. i don't know howthey get around the cycle. it's only from theobservation that they have cores

which are very different tothe rims of the diamonds, and so diamond often grows ona seed of preexisting diamond. and it's based on themodel that, you know, if the carbon isotopesare telling us that they've been subducted,then we have such cores and possible rims whichare not subducted. so that's all we know. it's not really proven. they've gone round thiscycle more than one time,

but theoretically,it's entirely possible. the oldest diamond wehave here is, i think, nearly 3 billion yearsold, 2.9 billion years old. a lot of diamond is in the 2to 3 billion year age range, so there appears to beone event on the earth, which produced a lot ofdiamond in the mantle. and this particular diamond of2.9 billion years is actually from a surface, geologicaldeposit is 2.9 billion years old, so it was already at thesurface and being weathered

around by 2.9 billion years. it could be a lotolder, as well. >> brilliant. well, that's all we've gottime for, i'm afraid, today. i'd like to thank you allfor coming, and thank you for your questions, as well. most importantly,if you could join me in thanking dr. adrianjones, thank you.