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Distinguished Lecturer Programme 2010–11

The Distinguished Lecturers for academic year 2010-11 will be Dr Jeff Harris (Glasgow University) and Dr Richard Harrison (Cambridge University).

The programme has the aim to promote interest and discussions across the broad field of Mineral Sciences (including all aspects of petrology and geochemistry at the Earth’s surface and at depth) the Mineralogical Society has appointed two lecturers, both of whom are good communicators and experts in their fields, to give lectures at universities and related institutions. The lectures will be aimed to appeal to undergraduates and research students as well as more advanced scientists. To promote the lectures, the Mineralogical Society pays the travel expenses of the lecturers; whilst the host departments cover any accommodation and dining expenses.

To apply for a visit by a distinguished lecturer in the 2010–11 academic year, please apply now (to the distinguished lecturer coordinator, Dr Martin Lee), if your department is interested in hosting either of these speakers in the 2010/11 academic year. Please send this completed form to Dr Lee.

Lectures offered by Richard Harrison

Lectures offered by Jeff Harris

Lecture A: Smashing diamonds reveals their origins

Systematic studies on the mineral impurities contained within diamond and on diamond itself, have provided major insights into the conditions within the mantle under which this mineral formed. Diamond occurs principally in two distinct environments called peridotitic ­and eclogitic and form over the depth range of 150 to about 700km, a zone which covers the whole of the upper and part of the lower mantle. Diamonds from >200km are relatively rare, the majority for both environments, forming in the subcratonic lithospheric mantle at about 5.0 - 5.5GPa (50-55kbar) and 1160 ± 100^°C. Within some of the mineral inclusions the analysis of radiogenic isotopes (Nd-Sm, Re-Os, Ar-Ar) indicates that the oldest isochron genesis age for peridotitic diamonds is 3520±170Ma, (Panda diamonds, Canada) with other determinations centred about 2000Ma (Premier and Venetia diamonds, South Africa). For eclogitic diamonds genesis ages are more distinctly episodic ranging from 2900Ma (Kimberley diamonds, South Africa), through 1580±60Ma (Argyle diamonds, Australia) to 990±50Ma (Orapa diamonds, Botswana). Trace element analyses, particularly of garnet inclusions, show that diamond formation is associated with the above rocks after they have undergone melt or fluid metasomatism.

Over 95% of the diamonds from the peridotitic paragenesis have carbon isotopes (δ¹³C) within the range –9 to –1 ‰. For eclogitic diamonds there is a much broader δ¹³C distribution ranging from –38.5 to +2.9‰. Both parageneses have dominant modes at –5 ‰, a value regarded as mantle derived. The isotopic patterns for peridotitic and eclogitic diamonds, especially when combined with the nitrogen content of diamond, can be modelled in terms of precipitation from closed system Rayleigh fractionations involving carbonate-bearing melts or fluids. Mineral equations such as enstatite + magnesite = olivine + cpx + diamond apply for peridotitic whilst dolomite + coesite = cpx + diamond would be eclogitic. In addition, open system fractionation involving CO₂ appears to be important for eclogitic diamonds to account for the extended tail of the eclogitic data.
 

In addition to these genesis reactions, the oxidation of a reduced species such as methane (CH₄ + O₂ = C + 2H₂O) has recently been shown to be an important reaction for some peridotitic diamonds. Although the present subcratonic lithospheric mantle is considered too reduced for this reaction to occur, if the genesis age of these diamonds (1900Ma) is considered, then these diamonds formed as a result of an ancient reaction which became less important through time, because of the common subduction of biogenic carbonates which made the mantle more oxidised.

Lecture B: Fingerprinting diamonds

Diamond classification schemes using such physical properties as shape, colour and surface features, help define diamond populations. Such schemes are not only useful in their own right, providing information about the trials and tribulations of diamond travelling from the upper mantle, but also can assist in diamond prospecting, particularly in linking alluvial diamonds to a primary source.
 

The humble carbon tetrahedron is the building block that enables diamond to create a multitude of primary shapes, some of which then undergo resorption. Diamond growth is usually episodic and patterns may be either straightforward (related to the external diamond shape), or be more complex, the patterns indicating that the final shape will be a consequence of more than one growth form. In other cases there appears to be no clear growth sequence at all.
The scale of any classification depends on the number and size of the diamonds available. Examination of large quantities of diamonds from known kimberlite/lamproite mines or alluvial sources, allows the classification of shape and colour to be determined as a function of size. Up to twelve shapes are used and resulting graphs are often distinct. Within southern Africa, for example, cube diamonds are prominent in the mines of Botswana, there are few if any octahedral diamonds in the production from the Letsing-la-terae mine in Lesotho and at the Swartruggens fissure mine in South Africa the so-called macle (the spinel twin of the octahedron) is unusually absent.
 

Diamond colour arises either through incorporation of atomic impurities during growth or through external influences acting on the diamond after growth. Nitrogen is the commonest atomic impurity and specific configurations make diamond either orange/amber or yellow. Small quantities of atomic boron make diamond blue. Body-green diamonds are rare, but a common variety at some mines is a green transparent coat. In both instances the cause is linked to radiation damage inflicted subsequent to formation. Brown in a diamond population is closely associated with plastic deformation, an event which occurs most likely during diamond residence in the Earth’s upper mantle.
 

Although eleven colours may be noted, classification shows that colourless, yellow, and brown predominate at most mines. Transparent green coated diamonds are found only in the upper oxidised parts of kimberlite pipes. In alluvial deposits green and/or brown spotted diamonds are often a feature, a form of radiation damage which allows an estimate to be made as to how long the diamond has been resident in that environment.
Surface features classifications divide into those restricted by a particular shape and those where the surface feature is unrestricted. Surface features are most diverse on resorbed diamonds where growth patterns can be exposed or on those from alluvial deposits where features due to alluvial transport are superimposed on those created in the kimberlite or lamproite.

Distinguished Lecturer Programme 2009–10

The Mineralogical Society Distinguished Lecturer series for 2009-10 is now complete. The appointed lecturers were Professor David Manning (University of Newcastle upon Tyne) and Professor Tony Fallick (SUERC, East Kilbride).

Lectures by Professor Manning

Lecture A: Mineral solutions to global problems
The world faces tremendous challenges to resolve the problems associated with climate change and food supply. In both of these, minerals have a vital role to play.  To achieve carbon sequestration targets of up to 8 gigatonnes per year, we have to consider reactions that may take place on a global scale, and one way to do this is to understand and exploit those that take place in soils, recognising the role of plants as a carbon sink that links the soil and the atmosphere.   To provide the ‘bottom billion’, the poorest of the world’s population who struggle to raise subsistence crops let alone commodity crops, we need to exploit the natural processes by which soil minerals provide essential nutrients as an appropriate companion to conventional fertiliser use.  In these and other areas, minerals have a vital role to play in sustaining the human race.

Lecture B: Minerals in biological systems
As a mineralogist surrounded by biologists, I am often asked “what do minerals do?”   Despite the widespread perception that they just sit in glass cases in museums, minerals are of course dynamic components of the biosphere, as any creature with teeth, a skeleton or a shell can tell you.   Even the silent plants depend on minerals within their biomass to perform specific functions on which they depend for their existence.   What is remarkable is the way in which biological systems influence the rates of growth (and dissolution) of minerals.  For example the antlers of a red deer, cast and regrown annually may weigh several kg, requiring ingestion and mobilisation of normally poorly soluble Ca and P on a timescale that is instant from a geological point of view.  There are many other examples of remarkably rapid mineral reactions within both the plant and animal kingdoms, and of course microbes also interact closely with mineral systems.

Prof. Manning spoke at:

• School of Geography, Earth and Environmental Sciences, University of Birmingham

• Geographical, Earth and Environmental Sciences, Keedleston Road Site, University of Derby

• Dept of Environmental and Geographical Sciences, Manchester Metropolitan University

• Camborne School of Mines, University of Exeter
   

Lectures by Professor Fallick

Lecture A: The oxygen and hydrogen stable isotope geochemistry of gemstones
Gem deposits offer particularly interesting challenges to the geologist:  because they are relatively rare, unusual circumstances are necessary for their formation.  Stable isotope geochemistry is one of the tools with which we can investigate these exceptional geological conditions.  Apart from the intrinsic scientific interest of understanding formation mechanisms and conditions, such research can also elucidate genetic models to guide exploration and exploitation strategies, and identify diverse contributions to placer deposits.  As an aid in constraining provenance, stable isotope ratios may have application in fingerprinting conflict minerals and materials.

The stable isotope (¹⁸O/¹⁶O; D/H) composition of silicate and oxide minerals is usually a function of the temperature, isotopic characteristics and chemistry of the parental fluid from which they precipitated.  The oxygen isotope fractionation factor between the fluid and the mineral depends on the environment of chemical bonding in a reasonably well-understood way.  The application of such concepts to the precious stones emerald, ruby and sapphire is now established, and progress is being made with newer favourites such as red spinel and green garnet (tsavorite, tsavolite).  The approach has proven particularly informative for semi-precious varieties such as agate and amethyst.

Lecture B: Planet Earth’s mid-life crisis: Carbon isotopes, concretions and the “Great oxidation event”

Around 2.2 billion years ago, the Earth experienced a series of dramatic upheavals which accompanied the transition from a reducing to an oxidising ocean/atmosphere system.  The global carbon cycle was perturbed to an extent unparalleled before or since, with the changes documented in the stable carbon isotope record of carbonate (δ¹³C_carb).  From concretions in sediments, there is evidence that the manner in which organic matter is remineralised underwent radical change.  However, the exact sequence of events leading to this “greatest pollution event of all time” (Lovelock) is not yet clear, and several aspects are paradoxical.  It is an open question whether there was one or several excursions to high (δ¹³C_carb); the end of the high δ¹³C record is reasonably well-established at 2056 ± 6Ma, but its inception is not well defined, so that only a minimum duration (~ 140 my) is known.  The interplay of the records of oxidised carbon (as carbonate) and reduced carbon (as organic matter) is especially problematic.  Recent drilling in Arctic Russia by the International Continental Scientific Drilling Program FAR-DEEP Consortium has produced a marvellous new archive of 3.6km of drillcore with which these and other issues are being addressed.

Prof. Fallick spoke at:

• University of Aberdeen

• Keele University

• University of Leeds

• University College Cork
   

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Distinguished Lecturer Programme 2008–9

In the 2008-2009 academic year, the appointed lecturers were: Prof. Liane Benning (Leeds University), and Dr Marian Holness (University of Cambridge).

Liane Benning

How to track the birth of a nanoparticle: the fight between kinetics and thermodynamics.
Nanoparticles play an important role in many terrestrial environments in the sequestration as well as cycling of elements, including toxic metals and organics. Their nucleation, growth and stability in near Earth surface settings can now be quantified using in situ and time resolved synchrotron-based approaches combined with high-resolution imaging techniques. Furthermore, the formation and transformation kinetics of nanoparticles and the mechanisms and effects that various metals or organics have on these processes will be discussed.

How 'Earthlings' have fun looking for life in a MARS analogue site: an AMASE'ing experience.
The NASA and ESA 'Search for life' Mars missions scheduled for the next decade require the development and thorough testing of stringent analytical protocols and low-detection limit technologies to enable the quantification of possible extant or extinct biosignatures on Mars. In this lecture I will discuss how such testing is carried out in extreme terrestrial environments of the arctic. I will also show how we have developed and applied field-based null-level contamination free sampling and sample handling, and have used spectral and microbiological approaches for high-resolution quantification of mineralogy and determination of low-level biosignatures.

Marian Holness

Towards an understanding of microstructural development in partially melted crustal rocks
Metamorphism commonly culminates in partial melting in the crust, with associated effects on rock rheology and mass transport. Teasing apart regional and contact metamorphic events may therefore be dependent on interpreting microstructures in partially melted quartzo-feldspathic rocks. These encompass a wide and potentially bewildering variation and in this lecture I will show how they are affected by time-scales and pore size.

A textural record of cooling in layered mafic intrusions
Textures in mafic rocks are traditionally used to distinguish between the early-formed liquidus phases (cumulus) and later phases which grew in the interstices of a crystal mush (intercumulus). In this lecture I will demonstrate how the details of grain boundary orientations within cumulate rocks record otherwise unaccessible information about the cooling history and throw new light on our understanding of the balance between latent and sensible heat loss during cooling.

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Distinguished Lecturer Programme 2007–8

The 2007-8 lecture programme is now complete. Visits by Prof. J. Blundy and D.J. Vaughan were well received and the project has been deemed a great success.

Lecture given by Prof David Vaughan

Minerals, metals, molecules and microbes: environmental mineralogy and sustainability
Metals have been central to human development since ancient times, and play a critical role in the cycling of elements at or near Earth’s surface. Understanding the cycles involving metals is important in studies of ore formation, pollution, and containment of hazardous wastes. Studies of key stages in the cycling of metals from the breakdown of metal-rich minerals, transport in solution or as colloids, uptake on mineral surfaces, and precipitation, will be illustrated with examples of work done in Manchester using state-of-the-art techniques.  These include atomic resolution studies of mineral surfaces and their reactivities using scanning probe microscopy, and investigations of the evolution of colloidal precipitates, or of sorption of metals on mineral surfaces, using synchrotron radiation methods. The importance of biofilm coatings on mineral surfaces will also be discussed, and also of relating phenomena at the molecular (or nano) scale to those at field, or even larger, scales.

Lecture given by Prof Jon Blundy

The subterranean machinations of explosive volcanoes
Explosive volcanoes are routinely monitored for signs of unrest. Deciphering the signals, such as earthquakes, ground deformation or gas chemistry, in terms of what is happening underground is not straightforward and rarely unambiguous. As magma chambers cannot be accessed directly our understanding of what goes on inside them is limited to studying their erupted products and attempting to link retrospectively the testimony of crystals and glasses to the pre-eruptive monitoring record. In this lecture I shall demonstrate the application of petrology to understanding past, present and future volcanic activity at Mount St. Helens volcano in the USA.