Report - XRD and MINERALS.

British Geological Survey, Keyworth, Nottingham, 15^th May 2008
Sponsored by:

Report on the XRF back to back meeting the previous day

Delegate Photograph

Morning Session

Chaired by the programme organiser - Martin Gill, Natural History Museum

Left to Right: Helen Maynard, Eric Ferrage, Caroline Kirk, Stephen Cairns, Jenny Huggett and Martin Gill (Chair).

Back in the splendid BGS meeting auditorium, after enjoying Martin Gill's Birthday party celebrations the night before, the audience (not all of whom were at the party) was treated to a morning of presentations concerning industrial applications of X-ray Diffraction that included a wine tasting session.

The first speaker was Caroline Kirk from the Department of Chemistry, Loughborough University and the Department of Mineralogy, Natural History Museum, London and her presentation was entitled;
Structural Studies and High Temperature Properties of Bismuth Vanadate Sillenites; Man-made Minerals.

Caroline explained that phase formation in the bismuth-rich end of the Bi₂O₃-V₂O₅ system had been investigated and an extensive solid solution of sillenite related phases found four temperature dependant polymorphs. These materials are metastable and have unusual high temperature behaviour not observed in other sillenite phases.

High temperature X-ray diffraction, differential thermal analysis and impedance spectroscopy were used to characterise their high temperature properties. Structural studies of this family of bismuth vanadate sillenite materials were performed using neutron diffraction data to try and correlate the metastable nature of these materials to their structure. The structure of these materials is related to the sillenite structure, but a new model was required to take into account Bi3+ partially occupying the tetrahedral site along with V5+ and the non-stoichiometric nature of the oxygen lattice.

It was found using DTA and impedance spectroscopy that conductivity also varied with changes in temperature. X-ray diffraction experiments with increasing temperatures show that at 750°C the system transforms from BCC to FCC and on cooling from FCC to BCC at 650°C.
On cooling there are 2 BCC phases, which are metastable - why? Perhaps there is a problem with the structure model.

From neutron diffraction, high temperature XRD and DTA studies it was proposed that the disordered nature of the oxygen lattice is the key to their metastable nature and different cations are being investigated.

The next speaker was Stephen Cairns from the WestCHEM, Department of Chemistry, University of Glasgow Department of Chemistry, Loughborough University and the Department of Mineralogy, Natural History Museum and his presentation was entitled;
Synthesis and Structural Studies of the Ettringite Group of Minerals.

Stephen discussed the importance of the understanding of the structure of etteringite and thuamasite in the application of civil engineering, specifically in the complex reactions of concrete. The formation of ettringite in setting concrete leads eventually to the formation of cracks; a famous example of this being the collapse of the Kepong Bridge in Malaysia.

The ettringite group of minerals have the general formula Ca₆X₂(SO₄)₃(OH)₁₂.26H2O, where X = Al, Cr, Fe and Si and the sulphate group can be substituted by carbonate or borate groups. Although the minerals are compositionally closely related, structurally they are different. Ettringite and thaumasite are the most important members of the group as they form in cement pastes, mortars and concretes. This has major implications for the construction industry and further study into the structure of these compounds is required to address this issue.

A systematic study of the structural chemistry of ettringite, thaumasite and their related phases is being undertaken using powder x-ray diffraction, single-crystal x-ray diffraction (for which a novel method of growing single crystals was developed) and neutron diffraction of both natural and synthetic s amples. A detailed phase diagram exploration is one of the aims of the group's programme and includes analysis of synthetic analogues of these mineral phases, so that migration of metal ions from the old to new structures can be studied and investigations into potential solid solutions that may exist between different members of the ettringite group.

The third speaker of the morning was Eric Ferrage from Laboratoire HydrASA, Université de Poitiers who presented:
Investigation of Smectite Structure Heterogeneities: an XRD Profile Modelling Approach.

Eric explained that smectite clay minerals in sedimentary rocks play an important role in water mobility and retention in soil or in waste repositories because of its high ability for cation and water retention. As a function of relative humidity and under non-saturated conditions, smectite shows a stepwise hydration behaviour corresponding to the intercalation of 0, 1 or 2 discrete sheets of water molecules in its inter-layers.
However, heterogeneities of charge location (between octahedral and tetrahedral sheets) and/or of charge amount (from one interlayer to the other or within a given interlayer) most often lead to the coexistence of different hydration states within smectite crystals. In addition strong positional disorder of interlayer water and cations has most often to be considered when attempting to reveal the structure of such disordered layered systems.

Isothermal X-ray diffraction (XRD) patterns were collected vs. time and the experimental structures calculated were compared to the standard models.

The following speaker was Helen Manyard from School of Physics, Centre for Science at Extreme Conditions, SUPA, University of Edinburgh and she presented:
New 'minerals' of the outer solar system - The high-pressure Crystallography of Methane

Very enthusiastically, Helen explained that here on Earth silicates dominate our mineralogy, but for both the Uranian and Neptunian systems a different, perhaps simpler, chemistry exists between H₂O, NH₃ and CH₄. Within the interior 'hot ice' layer of these bodies it is thought that interactions between these molecules account for the anomalous magnetic fields generated.

Methane's dissociation reactions could also be key to understanding what drives the planet's energy supplies. However studies of at these extremes of pressure (up to 25Gpa - 1Gpa at the bottom of Earth's oceans) and temperature have throw up inconstancies and the way forward is perhaps to understand how the constitute materials behave at room temperature.

In the suite of outer solar system 'minerals', H₂O, NH₃ to CH₄, methane is the sole organic member and the only one with no hydrogen bonds. Van der Waals and stearic repulsive interactions instead determine its solid structure and high-pressure studies can probe the interplay between these forces. The methane tetrahedron exhibits orientational disorder in many phases and the high-pressure behaviour of methane has been discussed in terms of a 'bad rare gas' model, leading to an assumption that at higher pressures it will adopt structures related the hexagonal closed-packed structure.

Studies have shown that this simplistic view of the molecule was incorrect and that the phase diagram is very complex, with eight distinct solid structures.

Using a diamond anvil cell to replicate the extreme high pressures required it was discovered that phase B of solid methane has 28,000 molecules per unit cell and so it is proposed that a new suite of minerals exist in the outer solar system.

The final and intoxicating speaker of the morning was Jenny Hugget of Petroclays with her fascinating presentation entitled the geology of Wine complete with samples - hurrah!

As a moderate but enthusiastic consumer of wine I never realised how important geology is to the growth of the vine (never gave it much thought really, until today). I shall pay much closer attention in future - anyway over to Jenny;

The role of underlying rock in viticulture is at least four-fold. It influences the soil type that forms over it, it permits penetration of vine roots to varying degrees depending upon the nature of the rock, it controls the geomorphology (slope) and it assists or hinders drainage of rainwater. In between each section and to illustrate each point of the presentation the audience was asked to participate in tasting wines from various geographical regions (for obvious scientific reasons, you understand)
However, as in many wine making areas the link between geology and wine quality is tenuous, some examples of spurious linking of geology and wine that have occurred was also considered.

One famous quote concerning terrain, "Of great importance to the wine maker, of very little importance to the drinker".

Types of soil for each grape;

So is it only a matter of climate? or are geology and terroir important when growing grapes for wine?

What the experts say about terroir

• Where there is a perceived marketing advantage in associating a wine with soil in a specific region the terroir concept is being exploited (Australian wine expert: Busby, 1825)
• The influence of the surrogates geology and landscape on wine rather than through the properties of the soil itself (French wine consultant Pomerol, 1989)
• A concept that originated in France. It is difficult to think of another country where it could have started, since it has features so characteristic of second-class French thinkers, a combination of the obvious (e.g. the quality of a plant depends where you grow it) and the mystical. (Hancock, 1999)
• Most scientists admit they cannot express quantitatively the relationship between terroir and the characteristics of wine produced from that terroir (Australian soil scientist: White, 2003)

The concept of terroir is implicit in the fanciful tendency to associate wine flavours with aspects of the soil or bedrock.

Perhaps the most widely stated is the supposed "flinty" character of Chablis wine. To a geologist it is difficult to imagine how a material as insoluble in normal groundwater as flint could contribute to the flavour of any wine, let alone what the flavour of anything so hard and insoluble could be. Equally fanciful is the suggestion that flint, schist and slate-bearing soils impart a "gunflint" character to Riesling.

Terroir: A delimited area with its own characteristic, geology, climate, methods of viticulture.

Geology influences:

At high latitudes sunny slopes have always been preferred for viticulture

In southern England where the angle of the sun is 62° at noon on midsummer's day a vineyard on a 30° slope will receive 8% more radiation than a vineyard on level ground. This may not sound much, but by October, during the final ripening, the difference is 30%.

Geological controls on soil chemistry and wine quality; Vines require all the usual plant nutrients (mainly N, P, K, Mg, Fe), present in well-maintained soil on any rock. Too much of any of them is a bad thing for vines. However in the Morgon appellation within Beaujolais the particular intensity of the wine is attributed to a vein of Mn ore that runs through the district

Iron availability:
In limestone the high pH of the pore fluid reduces the solubility of Fe, with the result that the Fe released by weathering becomes less available to plants. This is less of a problem for white varieties (which need less Fe) than red, and in the best limestones for viticulture there are sources of Fe. In the Chalk of Champagne the source of Fe is pyrite and in the Tuffeau of the Loire it is glauconite

Nutrient deficiency controlled by geology in Bourgueil:
In Bourgueil most of the Cabernet Franc is grown on alluvial sands and conglomerates with a low Fe content and this leads to chlorosis. The better vineyards are on middle Turonian Tuffeau Blanc

Geological controls on soil and wine quality;

• The parent rock type has little direct influence on wine quality" Wine Science, Jackson (1994)"
• The proportion of pebbles influences 1) drainage (good drainage is important) 2) warmth (absorbs heat by day, release it by night)
• The proportion of clay influences fertility and water retention (some is good)

Overdoing the importance of geology to wine quality?

• Chardonnay generally does best on alkaline soils (marls, clay with limestone)
• 1923 Premier Cru Chablis was recognised as being grown on Kimmeridgian limestone, while Petit Chablis could be grown on any other soil within the appellation.
• This was strongly opposed by some growers who said that orientation and altitude are as important and that some quality Chablis had always been grown on Portlandian limestone ….
• 1976 the reference to Kimmeridgian limestone was dropped from the definition of quality Chablis, while aspect and microclimate were added.

Importance of solid rock porosity and permeability

• Vines derive most of their nourishment from a depth extending down to 0.6 m, but will, most of the time rely on water from down as far as 2 m for transpiration.
• Only during periods of drought will they draw significant water from >2 m. At these times high porosity and low permeability will be an advantage.

Ideal water balance for vines

• Medium to high porosity ~15-45%
• High mass permeability >100 mD
• Low matrix permeability range ~1-100 mD

But is viticulture more important than soil or geology?

• Riesling is grown on schist in Alsace and nearby in Germany it is grown on slate
• Alsatian Riesling is typically both more full-bodied and drier than German Riesling
• Is this viticultural differences or subtle differences in soil? climate?
• In Alsace the wine is generally kept longer in barrel than it is in Germany
• And Alsatian soils are typically more calcareous and clay-rich than the German slate soils

All I can say is that I'm of to purchase a few cases of samples, isn't geology fascinating.

See if you can match the wine to the to the relevant section of the presentation......

Wines from the tasting - Left to Right: wines 1 to 4.

Richard C.E. Morris ,
Morris Analytical X-ray.

Afternoon Session

Chaired by the programme organiser - Martin Gill, Natural History Museum

Left to Right: David Beveridge, Melanie Sapsford, Andrew Hardy, Martin Gill (Chair), Peter Stacey, Alison Pawley and Stephen Hillier.

After lunch Stephen Hillier from the Macaulay Institute gave a presentation on the second survey of the National Soils Inventory of Scotland (NSIS). This included an overview of the importance of soil to the ecosystem and how it is affected by its mineralogy. Scottish soils differ from the rest of the UK in that they have a higher organic content, lower pH and are lower in nutrients. The minerals present are predominately quartz, feldspar, carbonates, iron oxides and clay minerals. These influence the soil properties owing to the nutrients they contain, their binding abilities, trace elements present, etc. The NSIS-2 is focusing on the variability of these properties on a local scale. Testing being carried out is bulk density, porosity, biodiversity, NIR, FTIR and XRD.
The soil samples are initially McCrone milled and then spray dried prior to powder diffraction analysis. Previous work has shown that side loading the samples in to the XRD slide results in preferred orientation some of which can be attributed to the operator. The spray drying on the other hand results in spherical "droplets" that pack randomly and are not influenced by the operator. This is seen by the consistency of the pattern when the same sample is prepared and analysed by different technicians. Full pattern matching is being carried out but this requires availability of the RIR data. The background is not modelled and an internal standard is not being used so as not to introduce dilution effects. The Macaulay Institute holds the National Soils Archive for Scotland with >40,000 air dried samples collected over 60 years.

Andrew Hardy from the University of Exeter followed on with a talk about cosmeceuticals. He explained that these are compounds that combine both pharmaceutical properties with a cosmetic role. Their first recorded use is believed to have been by the ancient Egypticians. A bivalve shell dated from 1300BC has been found containing traces of a green compound believed to be copper based. It is believed that cosmeceuticals are crushed minerals but there is so little sample left of these ancient materials that isotopic analysis is planned to determine if they are in fact naturally occurring or man-made. Modern day women in the Middle East still continue to use Kohls as cosmeceuticals which they do not realise can contain heavy metals such as As, Pb and Hg. So beware if you are given any of these as a gift!

A detailed history of chasing the blue mixed valence of iron sulphate was presented by David Beveridge. Its existence was first reported in the literature in 1843 by Barreswill. It was then again mentioned in 1863 by Lefort. However, David warned us, it is important to take 19th century reports with a "pinch of salt". In 1979 it was again reported in the literature by Steger. David has attempted to recreate this mixed valence state of the iron sulphate and was successful. However, it is only very transitory and lasted approximately 10 minutes before it decomposed in to a rhomboclase structure.

Everything then stopped for tea!

After a short break Alison Pawley discussed synchrotron studies of the structure of hydrous phyllosilicates (HPs) at high pressure and temperature. HPs are important in the Earth's mantle. They occur at subduction zones and take part in recycling water back in to the mantle. This water then affects the flow rheology of the mantle. HPs are soft and highly anisotropic. An example is talc, a magnesium silicate hydrate, which exhibits weak stable sliding behaviour. By increasing the pressure talc transforms in to a 10 angstrom phase that is likely to be involved in the transport of water in to the mantle to depths of up to 200km.
High pressure IR on the synchrotron ring using a beam diameter of approximately 10um showed that the frequency of OH stretching in talc increases as pressure is increased. This suggested there is no H bonding present in the structure. For pyrophyllite there was a decrease in frequency with increasing pressure suggesting the presence of hydrogen bonding. For both talc and pyrophyllite increasing the temperature led to a decrease in the frequency of OH stretching.
A deuterated sample of the 10 angstrom phase has been made in the lab. Studies on this material have not resolved the structure and it has led to a realisation that the structure is more complicated than at first believed. The data is still being looked at.

There is an international study taking place on crystalline silica. The reasons for this and the use of XRD in this study was presented by Peter Stacey in a presentation entitled accuracy in analysis - how much crystalline quartz do you think you have?
Crystalline silica causes silicosis therefore there is legislation related to its measurement. Samples of dust are taken from the air and collected on mini filters. These are then placed directly in an Xpert Pro MRD. The CRM used in this work, NIST 1878, ran out and was replaced in 1999 with NIST 1878a. Comparisons between the 2 CRMs indicated the crystalline phase in 1878a was 4% lower than certified. NIST then withdrew 1878a and re-issued it at 97% crystalline silica. This lead to people being very confused about the CRM and its value. Therefore, it was decided that this was an ideal opportunity to organise a comparative study.
There are a number of participating labs from France, Canada, Spain, the UK and the USA. The measurement procedure was developed by the French. Al or Ag peak is used for depth and absorption corrections. 7 "standards" have been tested from a number of countries. A number of different issues were raised and it was noted that as the particulate size increased the level of agreement between the labs decreased. Further analytical techniques were also considered including specific surface area by nitrogen BET and IR by KBr disc. From this work it emerged that there was a good correlation between the XRD results and those of SSA but not with IR.
Further developments planned include using Rietveld refinement on occupational hygiene samples.

The final talk of the day was given by Melanie Sapsford on analysis of non-marine evaporitic deposits of the Wadi Natrun in Egypt. Examination of the geological and archaeological samples helps to determine the role that sodium salts have played in ancient Egypt and how these relate to the changing nature of the Wadi lakes.
The Wadi Natrun is a valley 30 miles long and 50 km from Cairo. It contains a series of ephemeral evaporitic lakes of a non-marine origin. The number of lakes has changed with time and there are currently 12 lakes at present. The focus of Melanie's work has been samples from Lake Fazda. This is believed to have been around since Roman times based on the archaeological remains of glass manufacture found from that period. Chemical analysis of samples has included XRD, ICP and ion chromatography. The samples appear to contain high levels of burkeite, halite, some sulphate groups and some trona but none contain natron. Natron salts are known to have been used in the mummification process and it was hoped to find out which lake these salts have come from - obviously not Fazda.

Alison Burke,
Huntsman Pigments.

Last updated 29-Jul-2008

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