News post: 13th November
At the October meeting, member Tony Thorp gave a talk on “Diamonds”, in particular synthetic diamonds, but excluding gems.
The contribution which diamond research and particularly that of Loring Coes made to geology is little acknowledged; but his synthesis of some forty metamorphic and other minerals enabled geologists for the first time to establish the P/T phase diagrams so essential in working out the provenance of metamorphic rocks.
Anyone interested in gems and the story of how De Beers operated the most successful cartel in marketing history for over a century, should consult “The Death of the Diamond” by Edward Jay Epstein. It is a good read, and one of the few books on diamonds unsullied by output from De Beers and Ayers publicity departments. It is now somewhat out of date, so supplement it by searching for ”Element Six”, or go to www.e6.com (De Beers have always been coy about using their own name!)
Diamond possesses extraordinary mechanical, electrical;, optical, chemical and thermal properties which have made it a critical strategic material, particularly in times of war.
After Lavoisier and Smithson Tennant showed that diamond was indeed 100% carbon, like common graphite, researchers have endeavoured to convert the one into the other.
The discovery, in the 1870s, of primary diamonds at Kimberley in South Africa concentrated research into high temperatures and high pressures. James Hannay, Henri Moissan, Crookes, Parsons and others all failed, often in dangerous experiments ending in explosions, to produce diamond.
Before the turn of the century, the limit to achievable pressures in the laboratory was only some 2-3000 atmospheres. It was Percy Bridgman, regarded as the “Father of high pressure chemistry” and a Nobel laureate, who opened the way to higher pressures by inventing the “Bridgman Seal”, a simple device, based on the “de Bange” breach mechanism (invented in 1877 and still in use for the field pieces firing the salute on the queen’s birthday). With this device he defined the high pressure phases of dozens of materials, famously discovering ice VI, stable at 95 °C. However, although he squeezed carbon to over 100 000 atmospheres, he never produced diamond.
With World War 11, diamond became a critical strategic material and in 1941 GE, Norton Abrasives and Carborundum sponsored Bridgman in his efforts, however he was co-opted onto the Manhattan project and research was interrupted. (The behaviour of uranium and plutonium at high pressures was critically important at that time!)
With the breakup of the Bridgman team, Norton continued research on their own and their Loring Coes (of coesite fame) developed a simple pressure assembly comprising an Alundum (proprietary alumina-based ceramic) cylinder with a quarter inch bore and a steel reinforcing belt to keep it in compression. In the bore were top and bottom carbide pistons which could be used as electrodes and could apply pressure to a sample. If necessary, the sample could be surrounded by a carbon cylinder as a heating element.
With this device Coes proceeded to produce a whole series of minerals which were associated with diamond in kimberlites and eclogites, including garnets, pyroxenes, staurolite, kyanite, zircon, idocrase, tourmaline, beryl, sphene and topaz. He also squeezed quartz to 35000 atmospheres at 800 °C, producing coesite, which was unknown in nature at the time.Although Coes enabled the whole field of metamorphic mineralogy to be put on a quantitative basis, he never achieved diamond synthesis.
This was left to a team set up at GE as project “Superpressure”. The GE team included Francis Bundy, Herb Strong and Tracy Hall. The team worked very much as individuals and developed a series of different geometries of carbide anvils, retaining belts and gaskets. Some four years into the project, with no results from hundreds of experiments, most of which had a duration of a few hours, top management were considering whether to continue or not. This was a moment of truth and in a last ditch effort, Herb Strong set his apparatus up with a sample of “Steco” (a case hardening compound containing carbon and iron). He aimed at 50 000 atmospheres and 1250 °C and left it for 16 hours, overnight. Next day, he opened it up and there were apparently no diamonds, but he was interested in how much carbon was dissolved in the iron and sent a blob of fused material to metallurgy, for polishing and examination. A week later, metallurgy came back saying they could not polish the sample as it gauged up their polishing wheel! Eventually, two small diamonds were separated from the sample. It seemed they had succeeded. The next day, Dec 16th 1954, Tracy Hall set up his own apparatus in which the sample was contained between tantalum discs in the press and set to 100 000 atmospheres and 1600 °C and ran for 38 minutes. When opened, he saw dozens of diamonds stuck to the tantalum disc!
Strong’s result could not be repeated, but Hall’s was reproducible. Diamonds had been synthesised for the first time in a commercially reproducible procedure.
Meanwhile, out on a limb, in Sweden, the eccentric inventor, Balzar von Platen, working with the Swedish electrical firm ASEA developed a complex, expensive device comprising a cube packed with carbon, iron and a thermite mix, surrounded by carbide and steel wedges and miles of piano wire, in which he probably managed to produce the world’s first synthetic diamond in February 1953; but it was covered by a cloak of secrecy and the process was not revealed until after GE had announced their success. It is a mystery how this came about. It was either just commercial secrecy or possibly that they only discovered their small diamonds after the GE announcement.
So much is history, patents have run out and diamond presses are now commercially available for modest amounts. Diamonds are cheap and of higher quality than naturally occurring stones.
Even the amateur geologist can afford diamond hones, cutting and lapping discs for polishing specimens and making thin sections.
The industry has moved on and synthetic diamonds are now produced by several processes, including crystallising from plasma (CVD) and explosive processes. A once rare material is in everyday use and we are all the better for it.
The Next Meeting will be on Wednesday 16th November. This is the member's evening with Bill Bagley and Colin Humphrey guiding us through their visit to Iceland in 2015.
News post: 11th October
At the September meeting Dr Sara Metcalf gave a very interesting talk on Mesozoic mammals and mammalian evolution. Originally the finding of fossils of Mesozoic mammals and their immediate ancestors was fragmentary but since the 1990's many new fossils have been found, especially in China. The well-preserved fossils and the combined discipline of molecular phylogenetics have greatly enhanced the knowledge about mammalian evolution.
Using anatomical diagrams, cladograms and even a short YouTube video, Dr Metaclf took us through the evidence for evolution and the “family tree” of modern day mammals.
The next meeting will be on Wednesday 19th October when Tony Thorp will give a talk entitled “Diamonds from Peanuts...For Peanuts...And how Geologists can use them”
News post 14th September
At the August meeting David Pannett ( Shropshire Geological Society) explained how many of the landscape features observed in the Severn Valley are the result of glaciation. He explained how glaciations have occurred a number of times in the past 2-2.5 million years. The last of these being the Devensian from about 120,000 to 11,000 years BP.
The ice from these glaciations have given rise to many features to be found in the landscape, including moraines, kettle holes, outwash basins and river terraces. The origin of these features was explained. He took us on a trip up the Nant-y-Llyn valley to Pistyll Rhaeadr explaining the stepped profile of the valley, the corries and the classic hanging valley that is Pistyll Rhaeadr.
The talk was interesting and informative.
The next meeting will be on 21st September when Dr. Sara Metcalf will give a talk entitled: Mesozoic Mammals.
News post 15th August
Our next event will be on Wednesday the 17th of August, where guest speaker David Pannett from the Shropshire Geological Society will present his talk “Glacial Features in the Severn Basin”
News post 31st July
2016 Annual Weekend Field Trip – Lake District
The Club’s Annual Summer Weekend, 8-11 July 2016, was spent in the Lake District, based in the delightful lakeside town of Keswick, among the northern lakes, and admirably led by Cumberland Geological Society stalwart, John Rodgers. The Lake District, which is also the Cumbrian Mountains, is some 30 miles square of Ordovician and Lower Silurian rocks surrounded by younger Carboniferous rock. A band of Ordovician Skiddaw Slate lies across the north and a band of Silurian rock across the south of the district. Between them is a band of igneous rock, mostly lavas and ash flows, the Borrowdale Volcanic Group, hosted by Ordovician rock. This formed due to arc volcanism, caused by a subduction front as the Iapetus ocean closed only 40 km to the north, across the Solway Firth. An underlying batholith of granite caused the original uplift of older rock. During the Ice Age this erosion resistant dome was sculpted by glaciers to form the picturesque lakes and lakeland scenery.
On the Friday evening our leader gave an introductory talk on the lakeland geology. A month spent there would not do justice to the district, so our two days had to be very selective. On the Saturday we explored an area north-east of Keswick in the Skiddaw Group, around Mungrisdale and Mosedale Bridge, moving on in the afternoon to the nearby valley between the dramatic Bowscale and Carrock Fells. These localities allowed us to examine structures in the Skiddaw slate, and look at the effect of metamorphism on the slates, particularly rocks spotted with cordierite, and containing acicular andalusite. In the valleys of the Caldew and Grainsgill Beck we could see both granite outcrops and glacial action. The weather was mostly kind but, this was our twelth annual weekend excursion, and we can’t expect perfect weather all the time. It literally blew a gale when we walked up to the Tungsten mine. Saturday evening ended with a discussion back at the B&B before the group dispersed to various Keswick restaurants.
Sunday began at Friar’s Crag looking south down Derwent Water and discussing the working of the glacier which formed this, generally flowing north towards us, round the dolerite intrusion on which we stood, continuing north of us to excavate also Bassenthwaite Lake. This area is on the northern part of the Borrowdale Volcanic Group, so again we were able to combine consideration of the local volcanics - this area was a caldera – with an appreciation of the extraordinary erosive power of the glaciers. We drove down the west bank of Derwent Water to see roche moutonneés, lava flows and columnar cooling among many other features. In the afternoon we walked the Rosthwaite moraines just south of Derwent water, in the glacial valley now occupied by the north-flowing river Derwent and its tributaries from Seathwaite and Stonethwaite to the south, endeavouring to understand the glacial movements which left this debris. Another splendid weekend ended on the Monday morning, for most us with a look at Keswick and the Threlkeld Museum just east of the town.
News post 31st July
At the last meeting Dr. Chris Simpson presented a snapshot of the geology to be found on the island of Cyprus. The main focus of the talk was the Troodos Ophiolite. Ophiolite is a fragment of oceanic crust and the underlying upper mantle that has been uplifted and emplaced onto continental crust.
The Troodos ophiolite was created during the complex process of sea-floor spreading and formation of oceanic crust and was emerged and placed in its present position through complicated tectonic processes related to the collision of the Eurasian plate to the north and the African plate to the south.( Geological Survey department cyprus) It is seen as the most complete, intact and studied ophiolite in the world.
With many good photographs Dr Simpson worked his way up through the stratigraphic column of the ophiolite commencing with the ultramafic rocks like harzburgite composed of olivine and orthopyroxene. Harzburgite along with dunite are interpreted as a “mantle sequence”, which represents residue from partial melting of the upper mantle. The next sequence was the layered gabbro with massive gabbro above. The gabbro is a residual of magma. During the slow cooling, the heaviest minerals lie in the depths, thereby creating the darker coloured gabbro, with light-coloured varieties in the higher layers. At higher levels and in small pockets, the products of this different crystallisation are to be found, known as plagiogranites or granophyre.
Above this is a sheeted dyke complex. They are pathways through which molten basaltic magma rose from the mantle to the seafloor where it solidified as a pillow lava. Some of the magma did not reach to the surface and solidified as dykes, consisting of dolerite. Above these are the volcanic rocks consisting of pillow lavas and lava flows. Basalts predominate in the pillow lavas and are characterised by large spherical to ellipsoid pillows. Their crust is glassy due to the rapid cooling but the insides of the pillows is honeycombed due to sudden expansion of gases in the lava.
The geology along with the wonderful weather makes Cyprus a lovely and interesting place to visit.
The next meeting will be held on 17th August when David Pannett will give a talk entitled: “Galcial Features in the Severn Basin.”
News post 8th June
Our next event will be on Wednesday the 15th of June where guest speaker Dr. Chris Simpson will give his talk “Cyprus Geology: a snapshot”
News post 23rd May
This month we had a talk by Jack Davies on “Reflections on Geomorphology”. It was much more than an investigation of the development Britain's geomorphology, more a geologist's life story. Starting with childhood freedoms exploring Britain by cycle, through student days, to theses typed in DS with multiple carbons, he had developed a deep understanding of the development of landforms and an appreciation of the uniquely diverse geology of the British Isles.
He described, from a personal perspective, the landforms resulting from the Cretaceous transgression of Wales, followed by Mid Tertiary uplift and the removal of the chalky deposits, with the initiation of drainage and erosion. Stripping back of the Mesozoic cover revealed a wave-trimmed peneplain, with superimposed radial drainage cutting down to the Palaeozoic rocks beneath.
Mid Tertiary uplift elevated the Welsh High Plateau and later negative changes in base level produced the Middle and Low Peneplains with consequent adaptation of drainage.
Later Pleistocene glaciations produced the 400ft, 300ft and 200ft platforms
It was a refreshing approach with no Powerpoint!
The next meeting will be on Wednesday 15th June when Dr Chris Simpson will give a talk entitled: Cyprus Geology: a snapshot
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