Natural Science - Ellensburg Blue Agate

hi I'm Paul husking and I'm gonna talk to you today about Alan's Berg's blue agate but before we get into that I'm gonna run you through agate in general let's get started so the first question is what is agate and I'm gonna spend a little bit of time on this you'll see some really nice photographs of agates like these ones though these are not my photographs these are taken from a very kind gentleman at the Scottish National History Museum who's well known for these these are his pictures not mine now these are taken by taking a negative the rock cutting it polishing it in photographing it if that's not already apparent to you so the international colored gemstone Association such a thing exists their definition of what an agate is is Cal Sidney quartets that forms in concentric layers in a wide variety of colors and textures that's pure description but then they add a little bit to this definition as to how they think agates formed each individual agate forms by filling a cavity in host rock and I'll come back to that a little bit later that's quite nice pictures are they yeah you can buy those on eBay probably about $50 for a very small slice if you're interested so we recognized agate in our daily lives some of us anyhow and here are some nice examples some nicer than others like this one here this is an ancient Chinese seal it's made out of solid agate if you lift it up the bottom you'd see this steel and scribed on the bottom and then there's the usual jewelry wind chimes and perhaps even a belt buckle and yeah right now that's a good point so these are these are definitely not real colors except for probably these ones here in the middle and just from let's sort of raise it a really interesting point and takes me on topic off topic but that's okay these are from Brazil and you can just tell by just the overall appearance so if you know a little bit about agates you'll be able to spot sort of right 75% of the time where these come from this color this deep purple or lilac and this blue that's not natural this this blue is not natural either these are dyed now there's a belt buckle web page and this this ladies midriff is showing on hundreds of photographs and but they're very nice belts and and I think you can probably even get one inscribed with the Confederate flag which makes it all that more interesting so the International colored gem Association their definition is is great for the layperson but as you might suspect people who get paid to think about this like me I need to sort of divide this up a little bit more so I'm going to give you a definition of what an egg it is using geologic terminology or nomenclature or nomenclature in okay right so it's a two-part definition it includes minerals and texture but notice in this definition I'm not talking about origins so just minerals and texture let's start off with the minerals so an agate is largely comprised of quartz chemical composition sio2 and it doesn't always have to have these other minerals but it can have them so there's a list of them here and the geology students will be translating the the chemical symbols into mineral names already right so calcite iron hydroxides if you're interested this is limonite grrrrrr tight and hematite does anyone recognize that one hey all right right so this mineral here contains two molecules of h2o in its sheath in its structural formula which is what that is didn't know you'll coming to class today did you this is gypsum fluorite and a range of alumina phyllosilicates otherwise known as clay minerals but mostly quartz you don't have to have these in terms of texture agates are concentric Li banded and on the outside you would see an ovoid shaped nodule some of the time most of the time but not all of the time so we've got this two-part our definition for what a negative and it's rather a strict definition as you'll come to see after looking at this slide so my question to you and I'm asking for answers is are these agates have a quick look at it bearing in mind the definition I just gave you and I'll sample this coffee okay how about this Oregon Thunder API this is probably a few centimeters across is that an agate no why it's a thundering yeah silly question isn't really okay well mineralogical II this is a court but texturally it's not concentric leaf and that it's just massive so it's not an agate how about this one this is banded all right but it's not concentric so where you have straight lines of of quartz in a nodule like this this is known as an onyx some people who may be people here know you know you cut these four here that's a little more tough right that's why it's there well let's have a look at it we've got quartz it's the mineralogy we've got bands and they're slightly wavy but there's still not concentric are they so now this is another magnet this is known as turkey a Turkish onyx and then it comes in these huge slabs if I stood next to that it would probably be up to about my chest from my feet to my chest that's really nice I think that was barred from a wall of some mosque somewhere so let's just go back to the minerals just to remind you of the definition of the International colored gemstone Association their definition starts off with kal Sydney quartz and I just want to talk about what kal Sydney is in reference to quartz in case you don't know so generally the chemical composition of all agates is sio2 if you did a chemical analysis that's what you would come out with you wouldn't know what the mineralogy was but you know what the composition was and the dominant mineral which is made from sio2 is alpha quartz and here's a phase diagram which shows the stability of alpha quartz relative to other minerals which have the same composition sio2 and these other minerals are polymorphs so polymorph of sio2 this is how you'd say it alpha quartz is a polymorph of s and for those of you want to know this is what a polymorph is so it's a mineral which shares the same composition as another mineral but the structures are different and there's lots of different polymorphs of sio2 this alpha courts better quartz treaty might cristobalite and alpha and better of each of these as well which you can't see because they're filled of stability in pressure versus temperature space is so small and then there's these other guys and there's a few more which aren't on there but it's probably no surprise to you that the main the main mineral of agates is alpha quartz because look where we are which can stand on a lava flow today and sample agates and we're at very low temperature at low eyes would burn our feet and we're at very low pressure otherwise would be dead so we're in the Alpha quartz stability field so before we move on from this slide Stesha fight occurs on Earth's surface you can go and collect that only the sites of meteorite impacts so where meteorites have come in or asteroids are coming and impacted the surface of Earth you get these very high pressures and the quartz if it happens to be there will transform to Steve a coma Zeitz are very interesting mineral diamond companies will look for colors aight because if you can find codes out in your rock you'll probably find diamond as well so we know what quartz is we know where it's stable but that doesn't deal with the Cal Sydney so the question here is what is Cal Sydney well Cal Sydney is cryptocrystalline Alpha quartz and bear with me because we're sort of stepping through this definition building it up to the point where you're really gonna pass the first course of mineralogy with flying colors so cal sydney is alpha quartz but it's got this extra qualifier it's cryptocrystalline and it doesn't always form these here like fiber bundles but it sometimes does and I'll show you a picture of this at the end so what is crypto crystalline crypto crystalline means that you cannot observe individual crystals even with a microscope and there's two other words which go into other contexts here the first is macro crystal and the second is micro crystalline macro crystalline means that you can observe individual crystals with your naked eye and micro crystalline means that you can observe individual crystals with a microscope but not with your naked eye and one of the agates which is going around has examples of both in fact two of them do the Mongolian one and also the Brazilian one who's got the Brazilian one which is the one it's more or less round there can you lots of way at the back there okay can you hold it way up above your eye level and turn it around so I can see it that's it right now the very middle of that there had some nice quartz crystals and these are macro crystalline but most of that as for all Brazilian agates most of it it's crypto crystalline alpha quartz which is formed in fibers twisted bundles much like a young girl's ponytail and this is known as Kel Sydney you with me good because there's more to come okay you can you can put that down now so I'm going to make a point about scientific value agates being so beautiful we're in the early days before the 1900s quite often studied by those people who were aspiring natural historians much like most of us in the room here's an example of a Scottish gentleman Hittle and he published on on agates he published his book in 1901 mineralogy of Scotland with a large section on agates he you know typical natural scientist he trained in in a variety of fields as a doctor became the professor of chemistry chair and professor of chemistry at st. Andrews University know and wrote these books about agates so in the early days of Sciences science was really coming into its own at least in after the Industrial Revolution agates were studied they were interesting but unfortunately in the last hundred years or so agates have largely been ignored by geologists to the point where if I tell people that I'm working on agates they'll laugh at me and what joking and I find this most unfortunate and very narrow-minded because as we've learnt from things such as Isaac Newton's apple tree great discovery can come from even the most ordinary and small things in our lives so people who laugh at agates are completely missing this story and I they're probably missing the story and many other things and don't even told politics with them yeah that's true we could move on okay so the very most striking feature of agates has recently been studied and being the subject of a lot of study by a lot of different people so Agatha's again are again becoming the study of natural historians I mean look at this guy here it's probably about 15 centimeters across and I don't even need to ask you what the most striking feature of of these agates are it's the concentric banding it just jumps out at you and it's that perhaps which makes it beautiful well concentric banding in the last ten years has been in agates has been extensively studied by those people who are trying to understand self-organization in natural systems that is how does a system which is just sitting there organize itself into patterns and we see this all over the place I mean this has industrial applications as well this probably is an area of science or technology which isn't touched by some consideration of self-organization or its larger theory chaos theory so this is a rather simple system to study you can consider it just to be one chemical component sio2 but it's self-organized clearly and you can start to describe this mathematically and understand the physics of how this happens however even though we can describe self-organization and agates mathematically you know this has reignited a debate about how agates actually form and this is a debate which was never settled in the early days and it's certainly not settled now and I'm gonna show you one slide this one about this debate before I move on so there are two sides or at least two very fast separated ideas about this and a variety of ideas in between I'll just tell you about the two which are at the far end the first one here this is a lava flow from Hawaii but it illustrates how people who hold to this idea of aggregate formation this is true of their idea they believe that agates form at the very same time that the lava flow which hosts the agates formed and their mechanism is is that this hot lava flow much like this one here would run over a a puddle of water and suck up that water and cause chemical change in the magma or the lava widgets which is are running over it they're forming a silica silica gel which would then crystallize to form the agates which you can collect if that's correct and there's a lot of evidence that suggests that it could be this is what I call the hot closed system the other side the other part of the debate is that agate formation occurs a long time after lava flow formation so you have lava flow formation that the lava sits there as a rock it's called called and you have waters which just happened to wash by and through the lava and deposit layers of of quartz or kal Sidney so that would mean then that looking at this agate here from Brazil you would have a an original void space shown by the shape here probably a gas vesicle in the lava which at some point later was wetted by a fluid which came into the lava and deposited this layer here and then maybe ten years later twenty years and years later some period of time later another fluid came in and deposited this layer and so on and so on and so on so you have an open system where fluids can come into the into a rock pass through and deposit a layer of quartz so here we have two very different systems a hot and a closed system happens at a particular point in time now here we have a cold system relatively cold it as you can still have temperatures up to several hundred degrees Celsius but that's relatively cold compared to that which is 900 degrees 1,000 degrees Celsius in an open system which can take thousands of years to form an agate and there are people who had okay one way or the other and quite verbally as well right so just just to remind you you know hot enclosed sin formation that means at the same time or cold and open post formation after the lava flow formation so without having consensus about how agates form it's a little hard then to really understand all of the textures and and all of the structures which you can observe inside an agate so I'm going to show you a variety of pictures now which show these what I think are quite wonderful stretches and to a geologist we could interpret these and we could understand how the natural system well it's the rock water system works but it's a little hard to really do that when there's no consensus about how these formed so I'm just going to show you some pictures it's it's really just like a slideshow of family vacations but you might get something out of it I I certainly do every time I look at it and again these pictures are taken from my friend in Scotland he's got a worse handicap than I do that is his accent right so here are some nice scottish agates and they have this thing called a tube of escape was originally described in the scientific literature as a I'm flush canal which means it's German and it basically means a sort of a like a river canal or an exit canal it conveys this sense literally it's a little bit different I know but this is what they look like right here and remember you're looking at this in section right it's been cut and polished but in your mind's eye you can extend this in and out of the plane of the board into the third dimension and you would have a tube which at some point would intersect the outer part of the agate nodule and into the rock system so here's another one here here here and this one here is almost intersecting the edge of the nodule and I guess I guess this is the easiest one to see you may be able to introduce or exit fluid through this channel so this is known as a tube of escape unfortunately it's got this word escape to it because it's implying that there was fluid here and it exited where it moved in this direction that may not have been the case right if you have this cold post formation you may be moving fluids in and rather than moving them out but these are not apparently closed systems they have clear preserved evidence of communication to a broader system or the rock which hosts them and those of you have got the agates out there now see if you can see tubes of escape and sure you can yeah it don't it's visually stunning isn't it and to me it's surprising that mineralogists would not want to study this it's easy and it's cheap now and it's visually its visually rewarding so remember again you've seen this in section it came out in three dimensions and had this ovoid shape originally but what you're looking at here in section what I believe to be stalactites so here here here I'm not sure about these could be a little bit different but certainly these guys here in the middle and I've got some more pictures here look at that I mean those are clear stalactites right and you won't be able to buy that one on ebay so I'll tell you again no one knows how these formed there's no clear consensus on how at its form in general and even if there was if you just pretend that okay it forms by the cold open system post lava flow formation mechanism if that's the mechanism you go with then it's still difficult to explain this texture so in detail close-up this is what they look like now if I just showed you that Jeff if someone said I'm taking you along to a Natural Sciences seminar they didn't tell you what discipline it was and I showed you that picture you might be thinking worm tubes or something like that you might be thinking organic right well that's what some mineralogists think too now that perhaps you have this void space in the rock it's filled with a fluid that's a nice little environment for some animal plant I don't know help me out biologists for something to live in there right and this thing might this thing might be long and mossy and skinny and forming a nice substrate for crystallization of quartz and that's probably what's happened here and here and along here and we'll listen so I mean look at that it's gorgeous isn't it I mean it's very hard to consider as a mineralogist how you actually do this without some kind of organic templating some kind of organism templating and in fact I could have put some pictures up here they're not so good and I didn't have permission to use them but there are some German examples where if you section down one of these supposed Stella types you can actually see a little curly structures which I believe are meant to be biologic as well but way out of my depth now what did I want to say about that now well the coffee is not that good but thanks okay so here are some other textures this guy here he's not so beautiful but it's scientifically it's very interesting because there are layers upon layers upon layers of of different minerals which have formed at different times people who study rocks geologists would call that a stratigraphy people who study minerals would call it a pair of Genesis so there are layers there's a pair of Genesis different minerals forming at different times and we can start off by having the nozzle a void space in the rock which was filled by this dirty stuff down here so this is a mixture of rock lining on from the vesicle and quartz or Cal Sydney so started off with that and then there was this outside layer which was deposited after that then there was the calcite and then there was this nice banded Cal Sydney here and then there was one and two different depositions of macro crystalline quartz so this is quite complicated and to my mind this would argue for a a cold open system post lava flow formation mechanism having said that this is from Brazil and that is where the best evidence for the the hot syn model comes from so yeah this stone more work to be done now this coexistence of Cal Sidney macro crystalline alpha quartz and calcite we see this in the Ellensburg blue agates as well and you'll see a photo of that soon and as a geologist we also talk about other things like structures and rocks um he's a fault right so fold is a offset on either side of a of a fracture here it is here so these layers have been offset up higher and of course what this means is that the there was movement in the rock after the agate was formed but there's also evidence in other agates that the Eggers formed at the same time as the rock was being stressed or strained whatever the right word is so there was it was there was movement and faulting going on at the same time before and after the agates formed so here's a nice what might be considered a fault and if it was a fault what kind of fault would it be geology students yeah kind of get in close it's a little steep for that right I'll leave that one with you Yeah right reverse fault and what about this one if this was a fault point here what would that be look at the drag yeah so I mean you got some really great structures going on here and you can interpret this in a broader sense like what here's the agate what can I see and how does that relate to the rock and how can I interpret geology and a broader scale so scientifically agates are interesting on on a variety of scales so yeah so we've had this sort of run through our agates in general introduce the the problems with really understanding how they form talked about the definition mineralogy and the tend the texture and now let's go on and talk about our very own home growing and just pretend I've got a Northwest accent our blue agates well yeah they're gorgeous they they are probably as good as the best ones you'll find anywhere else in the world now this guy here is about 15 centimeters across what's that and the other measurement yeah right okay and if you've been down to the Ellensburg bead and yeah there was a product placement if you go down there you'll see the other half of this so this here is a horn surface which is being polished in the third dimension it goes back around and wraps out it's about the size of a man's hand and I'm I guess the owner of this could probably get I can't remember the exact number but he'd get five $6,000 for that and that's the true color by the way it's quite nice this is off the internet it's not my picture that one don't know about the copyright either but that's a nice specimen and this is owned by a local gentleman I don't recall his name right now he was in the newspaper last year he's got a fantastic collection and this is one of his best samples and it's a strange one too because you've got this beautiful blue and I don't know if that's blue I don't know what you'd call it but it's that's blue that's violet this is green and here it's got this red color so this is really nice may not look so good to you but as someone who's trying to understand how they form having this variety in one specimen is very nice and if you would give that to me I'd happily cut it up and study it but I'm sure that's worth more than that one so in isolation the colors here have electronically been picked so these are accurate for these photographs but they range from this grayish blue which is now the most common Ellensburg blue that you'll find all the way down to this purplish blue I think the most expensive ones and the most valid ones that you'll find out in the field now have this cornflower blue color but you'd be really lucky to find those as well most of the time it's that I don't say anyone does this but I'm sure I'm sure people take these grayish blue Ellensburg agates and and back them and put them in a ring to make them look more blue buyer beware so these blue these blues are world-famous and Kittitas County and so much so so much so that it was even a newspaper article on them and I happen to we couldn't find the guy who was working on them so I stood in for him and you know economically just like in other parts of the world they're the agates do contribute to that to the local economy perhaps not so much here as I as I could but if you go down to some parts of Brazil Rio de Sol the whole economy is driven by by agates and and geodes and that's true for other parts of the world too so the late medieval economy of the western central western portion of Germany was driven by agates and you're holding one of those agates someone's holding it you isn't the general audience so this is a little bit artificial this next section because I presented this part at a conference somewhere else and no one knew anything about it so there may be a few things up here which are like obvious to you but they weren't obvious to someone else and I just lift it and that's part of the talk so description the Ellensburg blue agates generally not concentric we banded quartz and chalcedony are they agates then no I mean according to the strict definition and also the not strict definition of the colored gem Association they're not really agates so what they are though is massive kal Sidney so but we use the term Ellensburg blue agate in inverted commas to get around not being strict about it most persons are not oh yeah so that's kind of a little strange I should say not agate in a strict sense so where do they occur that's what I mean about like telling you the obvious named after the nearby town of yeah right okay I'm in trouble now all right and it's a something you may not have seen this is a section of the United States Geological Survey map of our part of the country Ellensburg is right here you can highly see it but there it is and that purple area there I think is Radio Hill and then there's a series of higher mounds as you go up to the east right so as everybody orientated okay so this is this is the railway lines that right yeah I wish you were in my class yeah okay so this road up here this is this takes you up to the the blue pass and somewhere about there is the Liberty cafe yeah yeah it's yeah you got it you got it right so this is that this one right is that what you mean oh really yeah okay so this here is the this is a tno a basalt and you know what we got bit of coffee here than they do there this is this is generally basalt you know we have some Columbia River basalts here but really the main part of this whole map here is these purples one on a purple kind of Pink's right so this darker pink here and here and there in there and this lighter pink here so these here are local gravels which got there from from the Yakima River moving its way in this direction so it's what are they called again yeah Fork gravels thanks for that these are the thought gravels and is two slightly different variations there's this one here which is comprised of bits of rock which is mostly being ripped off from the Columbia River basalts and then there's this one here in the lighter color which is comprised of bits of rock which is being ripped off mostly from the tno episode up here so if you're going to go out in the field and look for Ellensburg blue your best bet is to look along here in the lighter pink not here having said that the best Ellensburg blue finds as far as I know because I have never found any by walking out there I've found in these this yellow stuff which is yeah some people love that stuff but for me I can't grow flowers in it so it's not my favorite stuff but these are the official rocks dirt and gravel and it's old glaciated and somewhere around here you have dry river dry creek dry thank you right and this is a way of some of the best agates are found not in the pink stuff because what happened is these are later than that and these are derived from glaciers which have just dumped everything including reworked pink thought gravels yep I said that right so let me show you what the the the best examples is at least as far as I know of Ellensburg blue look like in the field so this is just a lovely field shot on a late fall afternoon looking back towards the west now you recognize this value right yeah right so the intersections are down here summer isn't it no here right this is the insect right right so this is first Creek up here you climb up the hill and you have this dead tree which forms a very nice frame for the photograph but you're standing on the tno a basalt that you know a basalt is not like the rest of the basalt which you find as you drive east in the state which is the Columbia River basalt that yellow episode is a different beast it's twice as old generally as the Columbia River basalts it's about 45 million years old and it's being altered by hot fluids hydrothermal fluids we don't know when but probably before 20 million years ago and that's because the surrounding rocks which were about that age have seen very little or no hydrothermal alteration so we've got this bracket and it's no surprise that these rocks are hydrothermally altered because that's why Liberty exists right because it's a gold mine mining area Gold hydrazone fluids so there is a association between the Tiano a basalt and the Liberty gold mineralization which is a little tenuous I'm not going to talk more about it just throw it out there so this is what the rocks look like in the field this is generally what it looks like this is what it looks like if you're lucky so to come back to this photograph mostly you have what is what I consider to be a rather what's the time please now they're a rather disgusting looking rock with vesicles where gas used to be when the rock was cooling and erupting and sometimes these vesicles are filled with Cal Sydney which has got this nice texture on it this is a buttery Idol texture sort of lumps like that and if this was a slightly bluer color it would not be in the rock anymore someone would have sampled it that's about four centimeters from bottom to top but the Ellensburg blues the best ones the ones that you have in your jewelry this is how they would look in the rock if you could find it so here's a couple more photographs now this here is part of the same outcrop which you saw there and you have veins of material running through the rock which are filled with quartz chalcedony and calcite and who knows what else I haven't had a close look at them now here are some void space which is being filled with quartz calcite calcium carbonate and some quell Sydney and here's a small little what some people might call it geode it's not completely filled in so maybe wouldn't call it an agate of Cal Sydney with a lot of space which used to be filled is just a little bit left with calcite so this Cal Sydney quartz calcite Association is quite common there are some other minerals in there but we don't want to talk about those today so moving on to the question of why is it blue that's the million-dollar question and unfortunately it's not really because otherwise it'd be rich because I think I've got it answered so when I first came to town and I was talking to people about this people said well it's blue because it's got some titanium in it have you heard that before well it's got some cobalt in it we heard that you heard something like that right so this isn't this was why idea there's an idea which has been in the scientific literature for some time that there is that's blue because of light scattering but no one's ever really worked on this idea to prove it or disprove it and another option for why the allensburg blue is blue is that there are some very very small mineral inclusions inside it which may contribute to light scattering but no one has done a systematic investigation of the Blues until now took a foreigner to do it okay so we start off we start off with petroglyph E or the Ellensburg Blues Patrol goofy is it's just a fancy word for looking down the microscope so what you do is you take your it sample you cut it very thin glue it onto a piece of glass so it doesn't move around and then you look at it down a special microscope it's a double polarizing microscope no one has a petrographic microscope or a polarizing a light microscope you've got a few options there take your pick so this is what it looks like you have fibrous bands of quartz bundles Cal Sidney you knew that right and didn't have to say that and there are one two or more quartz bands so this picture here which is one millimeter across field of view so one millimeter across this picture shows both the types of alpha quartz alpha quartz fibrous bundles otherwise known as Kel Sidney or alpha quartz single crystals here micro crystalline quartz this is what it looks like under the microscope if I could take your ring or your brooch or your earrings or something and cut it up and look in the microscope that's what it would look like and I have another picture at the end which is slightly nicer so people have observed for a long time as did I when I first got here that if you hold up the Ellensburg blue in your hand it looks blue but if you hold it up to the light and let the light transmitted through it to your eye you can see a reddish color has anyone seen this before yeah get a pinkish shoe right and that's what that's what local people use as a test for a good Ellensburg blue if it's got a pinkish shoe that's a good one and that's basically what you can do here with the microscope so these are enhanced specimen blue samples but in thin section there's a hint of red to them you can see this hint of red here and also here now for this one here on the right hand side you know why the coloration this one here on the right hand side there are lots of tiny little mineral inclusions which you can't see so it's just basically making the picture look dark and this scattered throughout here as well and look where it stops right there it stops so in this region here you've got lots and lots of little mineral inclusions which making it dark but in this region here where it's red or blue and hand specimen there are no mineral inclusions so there's a difference as to why this allensburg blue is blue and why this Ellensburg blue is blue now this on the left hand side a part of me is more common than this on the right hand side this is not very common this is right at the bottom of a piece of the agate where it's in contact with the rock so the rock is right here this here is in the middle of an egg it so it's that part of the agate which I investigate it to find out why why it's blue so the first thing I did was do an absorption spectra so you take a very focused beam of light and focus it on the sample and then collect the light that comes out the other side to see which wavelengths which frequencies of light have been absorbed and this is that's basically what's on the on the x-axis there it's basically wave length you can think of it in that way even though it says something different but it's its wavelength and the percent of absorption of the total amount of light that's come through the other side so a light blue band has an absorption spectra which looks like that very little absorbance but it's like half a percent so most of the light that you shine through you gastly collect at the other side that's not the case for a darker blue band it actually absorbs more light well that's not rocket science is it but what's important here is not what you see but what is missing what's missing from this spectrum is some very sharp Peaks like one there or maybe one there and maybe one there which would tell you that there was a element which was responsible for the blue coloration so if the cobalt or the titanium was responsible for the blue coloration you see some very sharp spikes they're not there so it's got to be something else but just to check just to make sure I took some allensburg blues and analyzed them by instrumental neutron activation analysis don't worry about that but it's it's a really nice technique for getting accurate low level analyses of trace elements and solid materials and fluids and also icp-ms it's another technique but both of these analytical techniques showed that trace elements are at such low levels in the Ellensburg Blues in the blue samples that they're they're probably not responsible for the blue color at all and Illumina here likes to hang around with silicon so when you have sio2 you'd expect to find alo something as well they're buddies they're about the same size lands and and about the same charge and you can easily take out a silicon and put in a aluminum but even that's not happening here so the next thing I did was imaging by a technique called cathodoluminescence and this is where you take a focused electron beam and bombard a polished surface and induce light emission back off the sample so the electron beam was bombarded on these polished services one of micro crystalline quartz and one of a blue-gray kal Sidney they had exactly the same composition but they got very different imaging characteristics this is this nice yellow brown so this is what you'd see with your eye if you look down the microscope this yellow brown color if you look down the microscope for this one when it's luminescing it has this weak pinkish CL it's orange on this display but it's actually pinkish so these these guys have the same composition so the cathode or luminescence differences can't be because a composition has to be because of something else and catherdal luminescence is sensitive to either composition or structure or both in this case it can't be composition because they're the same so the difference has to be due to very fine scale structural differences and you can actually also click spectra from these images and we did that and the only real difference is is that for the blue grey agate you get a extra peak in the spectrum at about 500 nanometers don't worry about that but what it tells you is that there is probably some amorphous silica that means sio2 which is not part of a mineral it's just a morphus doesn't have a crystalline structure and this turns out to be rather important and I'll show you a even better image of that soon and time is marching right on so I'm not going to throw more data at you but the would have been nice though yeah yeah would have been real good but okay so trying to get at why these have the have these different cathodoluminescence images same composition but different structures what I did is I took a really nice sample of Ellensburg blue and and cracked it open and then put it in a scanning electron microscope and imaged it by secondary electron microscopy and this is what it looks like right so take a second to take it in that's your second right so what it looks like this is a broken surface you can see a few plate like structures here kind of like sheets of paper stacked on top of one another but overall what you can see it's tiny little balls right you see that little spheres there's another one they're all over here just all over the place it's it's my conclusion that these little spheres are the amorphous silica you know which is responsible for that 500 nanometer peak in the cathode or luminescent spectra and if I showed you the other set of data for having quite don't worry about it it's consistent with that data to look at the scale here two micrometers this is really really small that's to one thousandth of a millimeter so these little spheres are absolutely my new you could never see them with your eye you could never never see them with a light microscope because it's beyond the resolution of of light basically and don't worry I'm nearly finished so what I did is analyzed the diameter of these spheres for 202 of them and if you added up the height of all of these here that is the frequency or the number of them it would come to 202 and looked at the distribution of the diameter of the spheres and now rather than talking about micrometers of change the units to nanometers so we've got a more manageable number so instead of talking about - we can talk about 200 or 100 or something so what you can see is that there's large distribution with a center somewhere around 75 80 nanometers believe me these are really small in fact they're so small that a large majority of them lights majority okay 35 percent of the spheres have diameters that are equal or less than 1/10 of the wavelength of light that's tiny and this is great news for me because what that means then is that those spheres which we've seen we've seen with the scanning electron microscope and we've seen with other ways of collecting data that these spheres are probably responsible for scattering light as other people have suggested but not proven and scattering according to the mathematical expression which was first described by this British scientist rally 80 or 90 years ago and what this means is that when you have very small particles about 1/10 wavelength of light when the light comes in and hits these particles it scatters in such a way that blue light is scattered more efficiently why is the sky blue same thing that's a rhetorical question we're not finishing until the answer the question yeah it it's the same process the sky's blue for the very same reason up in the Alpha atmosphere you have particles in 202 such things like this which have a diameter about the same as what we're looking at here 1/10 wavelength of light and they scatter blue light more efficiently than the others so the sky appears blue so whole day Ellensburg blue in hand specimen it appears blue the sky's blue hold the Ellensburg blue up to the light and let light transmitted through it and it's got this pinkish or reddish color to it equivalent to the sky is looking at the sky at sunset when the sky is low in the horizon and the lights coming straight through the atmosphere it's got this a reddish color right so it's the same physics there and I was gonna throw up that big formula there to prove you that I'm doing science but when I have to skip over data I'm doing science okay so these spare oyk I just showed you here are small much smaller than which are observe for precious opal here and the other thing too is that these this is rather random there's no definite pattern to it whereas that what makes opal opal you have this very nice arrangement of these spheres and in opal and because of that you get an another phenomenon occurring called opalescence or iridescent and that is when you hold it in your hand and move it from side to side you get this play of colors you know you change from greens to Blues to Pink's to oranges and back again you don't get that for the Ellensburg blues because these spheres randomly all over the place so in conclusion the Ellensburg blues are blue because of light scattering according to Raleigh scattering from these tiny little spheres of silica which are trapped between larger fibers or bundles of fibers and the Ellensburg Blues the formation conditions of the allensburg Blues is subject of an ongoing study right now and there's a undergraduate student in the department in the front row who's going to be studying this this summer but we've collected enough data to surmise at this stage that the allensburg blues formed according to the cold and open post lava flow formation mechanism and on the last slide I'm going to finish and open up for questions before I finish some more coffee it's a microscopic view of Ellensburg food yeah that's beautiful isn't it I might start selling these posters

Channel: Central Washington University

Views: 16,938

Rating: 4.8979592 out of 5

Keywords: science, Ellensburg Blue Agate, blue agate, ellensburg blue, 2006

Id: uWynBGqH5m8

Length: 54min 20sec (3260 seconds)

Published: Mon May 13 2013