first experiment photos

Yesterday I wrote about the effect of water saturation on the size of the crystals grown in my experiments. Today I've got photographs:



These are back-scatter electron images, which means that the brighter the pixel, the heavier elements present at that point (and the darker the pixel, the lighter the element). The bright ring-like objects are rims of iron-rich garnet growing on the seeds of Mg-garnet that was present in the powder before running the experiment. The bright dots of the same tone of brightness as the rings are new Fe-rich garnets growing in the matrix. As you can see, there is a pronounced difference in quantity and size between the two samples. Note the difference in the scale bars between the two photos.

water is important for growth, even for minerals

One of the joys about the learning to run experiments process is that one gets to learn the results of both intended and unintended phenomena. In my experiments the intention is to seal powder of known composition into gold capsules along with a sufficient H₂O and graphite to ensure that the chemical reactions which take place when we elevate the pressure and temperature (to simulate what happens to rocks buried at great depth) take place in “water-saturated” conditions (which is to say there is enough water available for the growth of minerals which require water as part of their chemical formula, such as the micas). However, learning to weld the capsules is a difficult process (I’ve got a draft post on that topic just waiting for me to get photos that actually display the features I want them to show).

As a result of my welding trials and tribulations I’ve had mixed success in the “sealing” part of the above paragraph. Despite the issues with my first attempts at sealing, we ran my first experiment nonetheless, giving two samples a week and a half at elevated pressure/temperature (in this case 650 C and 25 kbars). Once they were “cooked” we had the gold capsules mounted into small disks of epoxy, then carefully polished the disks until the insides of the capsules were exposed. During the polishing stage we received our first confirmation that they had not achieved the same level of “sealed”. Apparently when properly sealed the presence of water inside the capsules ensures that the pore space in between the grains of powder are occupied, and as a result even the high pressures to which we subject them aren’t enough for the new minerals to properly interlock when they grow. As a result, while there are new crystals present, the texture isn’t very rock-like, and when polishing it is easy to accidentally remove clumps of the sample itself. This is the texture we were anticipating, and, for one of the samples run in the first experiment, this is exactly what happened. In these cases we polish only enough to just expose the inside of the capsule, then add more epoxy, letting it soak down into those pore spaces and let it dry before completing the polishing process without so much risk in losing what we are trying to polish.

However, in the other of the two samples run in the first experiment I must not have done the final welding properly, because the contents of the capsule were much harder, and held together better, meaning that the pore space was not held open with fluid when the minerals were growing. This was obvious during the polishing process, so I was able to go quite a bit deeper into the capsule (remember these are only 2 mm in diameter and about 5 mm long so “deeper” is only a relative term) before needing to add the additional epoxy.

Today we got to look at these samples in the microprobe, and as expected from the difference in their textures noted while polishing them, they are rather different from one another. The one wherein I had issues with the welding did contain some water; we know this because there are very small grains of mica present. However, neither was it water-saturated, so it lost some due to the poor seal of the capsule. It contains many, many very tiny grains of garnet (~1 micron diameter; remember that there are 1000 microns in every millimeter) which nucleated on their own, and very thin rims of garnet on the “seeds” which had been included in the powder to encourage garnet growth. The rest of the sample is even finer grained “matrix” minerals, which are going to be difficult to analyze. The other, water saturated, sample contains fewer, larger, grains of garnet, and the rims of new garnet growth on the “seeds” are much thicker than in the first sample. While it, too, is generally fine-grained, it will be easier to find single crystals large enough to get a good analysis of their compositions (which we need if we are going to accomplish our goals).

Having had this first look at the samples we’ve set the probe to create “element maps”, pretty full-colour pictures showing which areas are high (warm colours) and which areas are low (cool colours) in specific elements. Once we have these maps, we will use them to select the grains for the detailed compositional analysis. But even before we do that, I now have a better understanding of the difference between water-saturated and water-under saturated environments in terms of the ease at which minerals grow.

Attending AGU in December

While others in the geoblogsphere are still posting about their adventures at GSA in Portland, I’ve just booked my flights for AGU in December. Anyone else planning on attending that one? It would be nice to make it to one of the geoblogger meet-ups instead of reading about them from the far side of the planet…

Extending the parameters of my “1000 words a day” challenge

Starting in June of 2007 I set myself the goal of reading 1000 words a day from the geologic literature. The reason I chose to do this was the fact that I had a huge pile of papers I needed to read, and hadn’t been making the time to read any of it. Since then there have been numerous days in which I forgot and had to start over. My count has ranged from a low of accomplishing it two days in a row before missing a day to a high of 118 days in a row (my current count is at 42 days, which is the record for the 113 day period since arriving in Europe to commence my first post-doc position). Last night as I was finishing up my evening yoga in preparation for going to sleep I realized that I’d not yet read my 1000. I further realized that my computer and all paper copies of journal articles and textbooks I currently have in my possession were across the street in my office (I love my 2-minute commute to work!). I considered walking back over to do my 1000, but then I thought about the spirit of the rule. The goal was go get me to read a little bit, every day, so that I actually made progress and stayed current with my self-learning.

One of the things I’m doing here, in addition to my experiments, is taking classes in the local language. I’m dutifully doing my homework each day before it is due, but I’ve not been making much additional effort towards actually learning this language. All of my colleagues are so fluent in English that I can speak at my normal high rate of speed, so I don’t *need* to learn the language to do my job. Likewise when at the market it is easy enough to use the phrase I’ve memorized for “half kilo” and point, and then look at the numbers printed on the cash register to work out how much to pay. Again, I don’t *require* the local language to live my life here. Yet, it would be nice.

Therefore, I have expanded my “1000 words a day” to now be either read (at least) 1000 words of geologic literature in my own language, or spend 20 to 30 minutes translating something. One of my favourite books as a child was Anne of Green Gables . I have read, and re-read that book on numerous occasions. I also own copies of it translated into other languages. I purchased the version in the local language soon after I arrived. Prior to last night I’ve only “read” it—by which I mean open the book and look at every word, forming the sounds they make (either in my head or out loud, depending on if another is present), and looking for words which I can understand due to their similarities to the English equivalent. There are just enough of these that I am able to tell where in the story I am based on my memory of the original text. However, while doing this helps me to get a slight feel for the flow of this language, I’m not learning much. Therefore last night I went back to the beginning and actually took the time to write down each word I wasn’t positive I understood, and looked it up in my dictionary. The first two sentences of the story are long and complex and a half an hour elapsed while I looked up the 23 words I didn’t already know. I then read them out loud once straight through, then again phrase by phrase; pausing to state the English equivalent of each before reading the next phrase. It didn’t help me learn new thing in my primary field, but alternating this technique now and again with my normal 1000 a day will help me better fit into this country in which I’ll be living for another year and a bit, and so, I am happy with this change to the “rules” of the game I’m playing with myself.

Background learning has meant a reduction in posting

As the weeks slip by in my new job I find that I’ve not been making time to post. I do have a couple of draft posts which are waiting for photos to illustrate them, but they’ve been in a holding state for ages. Somehow the daily press of learning new skills, applying them, attending language lessons 6 hours a week, and doing the homework, combined with a half-hearted attempt to develop a social life in my new country has conspired me to feel as though I can’t spare the time for posting here. However, my log of manner in which I am spending my hours indicates that I have been making plenty of time for personal e-mail and reading the blogs I follow. In theory some of that time could have been spent writing instead of reading.

Ah, writing; it is such an easy way to communicate with people—simply enter the words into a keyboard at a time of your own choosing, and your audience will have the option to read it later, at a time of their choosing. No need to arrange a face-to-face meeting with them to share your information. No need to repeat yourself over and over—one typing session can communicate to hundreds of people, should you wish it to (and, at times, even if you don’t so wish, so it is always best to be careful what you commit to the written form, lest your words be shared in a venue unexpected).

So, what science have I been doing while I was busy not writing (or, in a couple of cases, not taking the photos to accompany the writing)? So far it has been simply learning the mechanics of setting up my experiments. #1 has been run, #2 is in progress, and #3 is approaching ready to go. Next week, I am told, we will look at the results of #1 in the microprobe and see what there is to see. It will be interesting to compare the two samples. My experiments are being run with about 5% H₂O and a small piece of graphite sealed into the gold capsules with the powder. When sealing the capsules it is important to do the welding with the capsule bottom surrounded by water to keep it cool so that the welding process doesn’t boil off the water before it is sealed. I failed to do this with the first capsule I filled. Likewise, I am not certain that I actually managed to get the capsule completely welded shut. If there is a small opening in the capsule it is possible for the water to boil out of the capsule early on in the experiment, and so not be available for chemical reactions.

Given the huge difference in texture between the two samples which comprised my first experiments, this may have happened for one of them. Apparently when water is present in the capsules the result is an amount of porosity in between the grains of powder, despite the high pressure of the experiment, so the end product is soft and easily torn out of the capsule after the run, if one isn’t very careful in the polishing process. However, when water isn’t present the grains of powder are pushed more closely together, and the new minerals have a chance to interlock as they grow, resulting in a much more coherent sample. One of my two samples polished up without a tendency for powder to be plucked out of it, so it is likely that this one operated under “dry” or nearly dry conditions. The other required much more care as it was soft. It was necessary to coat it with additional epoxy before the final polish to keep it from being lost. It will be interesting to compare the results of the two samples. Are there any hydrous minerals at all in the one we suspect was “dry”? I will have to wait till early next week to learn the answer to this question.

Learning to create capsules for experiments

Having recently started a position as a post-doc with an experimental petrology team it is now time for me to make the transition from reading a huge stack of background material to actually doing experiments. This requires learning a whole new skill set, like welding. Here follows the notes I’ve made on the first few steps of creating sealed capsules full of material to be taken to elevated temperatures and pressures during my forthcoming experiments. This is mostly for my own information, but someone out there might find it interesting or useful (or have helpful comments they can add), so I’ll share it here.

*Step one: Prepare the holder in which the capsule will be placed while filling it

During the filling process we use small metal disks into which holes of varying diameter have been drilled as a holder for the capsules (different sized holes are needed because different experiments use different sized capsules). First find a disk which has a hole with the correct diameter (or make a new hole in a disk if necessary). It needs to be just big enough to insert the tube into, without being loose. Then use fine sandpaper to carefully polish the metal around that hole so that when you get to step 6 you will have an easier time of filling the capsule.

*Step two: cut the tube for the capsule

For my experiments I will be using capsules made of gold tubing that is 2 mm outside diameter (1.4 mm inside diameter).

Obtain the correct diameter and metal tube (our lab uses both gold and platinum/gold alloys in a variety of sizes, I’m to use gold for mine) and then cut off a ~7 mm length from one end. To cut the tubing place it on a metal plate, then place an x-acto blade upon the tube and use the blade to exert a gentle pressure to roll the tube back and forth until the blade cuts through without squishing the tube. The back-and-forth motion is essential. This is not “sawing”, which uses a serrated blade to tear chunks out of a material which is stationary, but rather the tube itself rolls during the process as the blade slowly cuts into it.

*Step tree: Pinch closed one end of the tube

To seal the first end of the tube use pliers which have slightly rounded side edges. It is important to use the correct tool, as the sharp sided pliers can pierce a hole in the gold between the unpinched and pinched portions of the tube. (However, one of my colleagues uses the straight-sided ones, but he is very, very careful.) We use a three-part closure, which looks much like a symmetrical peace symbol. In order to create this do it in stages, don't try to squeeze it to final tightness on the first go, that won't work. Instead do a little at a time, slightly pinching on one side, turn the tube 1/3 of a rotation and pinch again, repeating around the tube, tightening the pinches a bit more each pass. Ideally, one wants it to be closed all the way to the center without leaving a hole at the triple junction. Unfortunately, this is difficult to achieve when working on such a small tube with pliers which are so much larger than the tube. Once the end is pinched shut trim the three edges using a cutting tool with beveled edges. The reason for wanting beveled edges to the cutter is so that the place where the two edges of gold meets is as narrow as possible, which will make welding easier. Hold the cutter at a slight angle so that once trimmed the triple point at the junction is slightly higher than the far ends of each of the three seams. (This photo, above left, taken through the microscope, shows a crimped tube held in place in the clamp and ready to weld.)

*Step four: Weld the pinched end shut

The voltage necessary for welding will change based on a variety of factors, including the diameter and length of the capsule, the thinness of the seam, the sharpness and length of the graphite in the welding tool, and what, if anything, you use to cool the capsule as you work. Unfortunately, our

welder isn't very precise and it can be difficult to adjust it to the perfect voltage for any given job. For this size we tried a variety of settings between 25 and 30 V, the 25 V was clearly too low--the welder left it looking "dirty" and coated with black, which is graphite from the welder being left on the gold. At 30 V it was too high; there is too much melting. In between that range the exact value was hard to find, and as variables change, so does the perfect voltage for the task. One variable which can make a huge difference is the sharpness of the graphite point. We have two different sharpeners, one of which makes a sharper point than the other. Using a “point” created by the duller of the two sharpeners at a voltage which isn’t high enough for that point and then switching to a point created by the sharper of the two sharpeners without turning down the voltage will result in the entire end of the tube melting.

The bit of advice I obtained the next day seems to have made a difference—don’t try to touch the gold with the graphite point, but rather hold it just barely close enough to cause an arc between them, and then try to draw that arc along the length of the seam. This isn’t easy, but I did wind up with useable results. Alas, the photo to the upper left doesn't show the welding very clearly--gold is just too darn shiny to photograph well through a microscope with a cheap camera when resting in a brass holder (this is after adjusting the brightness/contrast/intensity to make it visible at all).

I was also told that when welding I should try to start at the outer edge and draw the graphite point towards the middle, which brings excess gold from the edge towards the center to fill the small hole at the triple-junction. The goal is also to wind up with a flat bottom after welding.

*Step five: Prepare the welded tube for filling

After welding the tube it is necessary to re-shape the tube so that the capsule will have properly rounded/curving edges. We have a form (photo to the left) into which the tube is placed carefully so that the widest parts will be inside the form and not pinched between the two halves of the form (one chooses the correct diameter chamber within the form for the tube in question, of course). Once it is positions correctly the form is closed, and the tube is pressed back into a cylindrical shape. Once it has been re-shaped in the form it is put it into the holder (prepared in step one, and resting on a metal plate) and insert into the gold tube a small rod which has a diameter which just fits into the tube (in this case the rod needs to fit into a space 1.4 mm wide). Gently tap the rod with a mallet so that the bottom of the capsule flattens against the underlying metal plate and spreads out to match the curve of the sides of the hole in which the tube rests (take care as to not strike it so hard as to tear a hole in the gold tube!).

After much effort I now have three small capsules with one end of each sealed and flattened, and the other end still open and ready to fill. Stay tuned for steps 6 and 7 once I get them working. Having finally managed to get the tubes ready to fill, I chose to rest on my laurels and call it good for the day.

Pre-Conference Field Trip, Stop Two: Siccar Point

It has been nearly two weeks since I attended the Pre-Conference Field Trip, yet the memory of the day remains strong. I have already written about Stop One; today’s post continues our adventures as we follow in the footsteps of James Hutton, visiting the unmistakable unconformity at Siccar Point.

This outcrop is said to be one of the most significant in the history of the study of geology. Before Hutton published his theory on geologic time many people accepted Bishop Ussher’s calculations that the earth was only 6,000 years old. However, Hutton’s observations of geologic phenomena led him to realize that it must be far, far older than that to account for the sedimentary record. He observed erosion taking place in the world around him; saw how much sand a river can carry to an ocean over time, and reasoned that this process must have been going on for as long as there have been rivers. The rate at which the sand is deposited onto beaches or into lakes, or along a riverbed is measurable, and so estimates of the time needed to deposit a given thickness of sand may be calculated. He also noted that when sand is deposited by water, it always happens in horizontal layers. Comparing such layers of fresh sand, mud, and/or gravel with layers of sandstone, mudstone, and conglomerate leads one to the realization that the sedimentary rocks must have, at one time, been made up of loose sediment, before they became compacted and/or cemented into solid stone, and any sedimentary rocks which are folded or tilted must have been tilted or folded at some point after deposition and after becoming rock (or the sand would have slid back down into flat layers again).

The rocks in southern Scotland include two very different packages. The older of these packages is made up of Silurian sediments—poorly sorted sandstones (greywackes) which have been folded intensely enough that the bedding now stands on end in many locations rather than horizontally. The younger package is the “Old Red Sandstone”, which was deposited during the Devonian. Hutton knew from his explorations in the region around Edinburgh that the red sandstones are reasonably flat-lying and outcrop to the north of the steeply tilted Silurian greywackes. He knew that there must be some place where the two rock types are in contact with one another, so he and some friends set out in a boat along the coast in search of it.

One can imagine the delight felt by his party when they discovered that contact, at Siccar Point. While it had been possible that there was a gentle transition from the steeply dipping sedimentary rock to the south into the flatter lying sandstones to the north, what they discovered was no gentle transition.

Instead they discovered evidence that the older rocks must have been deposited as typical flat-lying sands and muds of great thickness, transformed into rocks and folded so tightly that the layers now stand on end, the edges of the folds and some unknown amount of rock eroded away, and then, some time thereafter, the sands which were to become the “Old Red Sandstone” deposited atop them, before themselves becoming rock and then being subjected to erosion. Hutton argued that if sedimentary rates in the past operated on the same sort of time scales as they do today there is no way that all of that could possibly happen in so short a time as only 6,000 years. One of his companion on that trip, John Playfair, is recorded as having said that “The mind seemed to grow giddy by looking so far into the abyss of time” when they contemplated just how much time the entire process would have taken.

Indeed, what they couldn’t know as they stood upon this rocky shore contemplating "deep time" was just how much time is represented by just the period of erosion between the two rock units, which has subsequently been calculated at fully 55 million years, during which an ocean basin closed and a mountain range grew.

Unlike Hutton's first boat-trip to this location, our field trip approached the point by bus, traveling south from Edinburgh, and finally stopping in a field near the coast some 55 km to the east of Edinburgh. Travellers are greeted at the stop with a first information sign at the trail head,

and a second when one reaches the point at which one descends to the seaside.

The way was steep, but, fortunately, it wasn’t a rainy day, so the grass was dry, and we made our decent safely.

We then spent a pleasant time examining the rocks, and taking photographs before climbing back up the hill to return to civilization, content in our own observations that yes, indeed, this outcrop does record simply amazing amounts of time.