Analysis of Serpentine Polymorphs by Vibrational Spectroscopies

Celine Lemaire (lemaire@lmcp.jussieu.fr)¹, Francois Guyot (guyot@lmcp.jussieu.fr)¹, Bruno Reynard (breynard@ens-lyon.fr)² & Jean-Luc Boulmier (boulmier@exchange.brgm.fr)³

¹ 4 place Jussieu, LMCP, case 115, tour 16-26, 75252 Paris cedex 05, France

² Laboratoire de Science de la Terre, ENS Lyon, 46 allee d'Italie, 69634 Lyon cedex 7, France

³ BRGM, 3 avenue Claude Guillemin, Orleans la Source, 45060 Orleans cedex 2, France

Serpentine polymorphs, well characterized crystallographically; have been studied by vibrational spectroscopies: mid infrared (MIR), near infrared (NIR) and micro-Raman. A careful analysis of OH stretching modes, in the 3500-3700 cm^-1 domain, is particularly useful for discriminating among different serpentine polymorphs, and with other minerals possibly present in the samples, natural or synthetic. First, we show that MIR and NIR spectroscopies may be used for asbestos detection in complex building materials, especially for chrysotile which is the common fibrous facies of Mg-serpentine. In-situ analysis of building materials is faster and easier with vibrational spectroscopies than with transmission electron microscopy. Indeed, a portable apparatus in NIR domain, PIMA, proves to be a good detector of chrysotile, especially in asbestos-containing floor tiles. MIR, which is used in attenuated total reflexion mode, does not require specific sample preparation and allows chrysotile detection in materials. We determined the detection limit of NIR and MIR spectroscopies by analysis of synthetical materials (plaster and cement) with known concentrations of chrysotile. This limit is about 1 wt.%, depending on the occurrence of other interfering minerals. Some specific cases in which vibrational spectroscopies cannot be conveniently used for asbestos detection will be discussed. Second, we show that the different serpentine polymorphs can clearly be distinguished by MIR spectroscopy and micro-Raman. These polymorphs are lizardite, chrysotile, antigorite and polygonal serpentines (picrolite) which have planar, cylindrical, corrugated and polygonal structures, respectively. It therefore appears that vibrational spectroscopy is sensitive to the fibrous character, an important point in asbestos detection. The OH range being the most discriminant, the assignment of the OH bands and shoulders has been improved by a high-pressure Raman study in diamond-anvil cell up to 10 Gpa, as well as by measuring the effect of experimental D/H substitutions.

An Alternative Method for the Measurement of Thermal Conductivity of Basaltic Melts

Christian Lenk (zimano@mail.uni-wuerzburg.de), Ralf Buettner & Bernd Zimanowski

Physikalisch Vulkanologisches Labor, Institut für Geologie, Universität Würzburg, Pleicherwall 1, D-97070 Würzburg, Germany

Cooling of magmatic melts and energy transfer to the environment are controlled by the temperature dependent thermal conductivity. Despite of this importance, only a few (partly contradictory) investigations on thermal conductivity of silicate melts in the partial molten state can be found in literature. As an alternative method for the determination of thermal conductivity we used viscosity measurements during quasi-stationary cooling of basic and ultrabasic melts in the newtonian flow regime. From these data the heat flux can be calculated after calibration of the set-up with a melt of known thermal conductivity.

Three melt compositions (olivine nephelinite, shoshonitic basalt, tholeiitic basalt) were remelted, homogenized, and measured in a static argon atmosphere (atmospheric pressure) in the temperature range between 1100 and 1350°C. The respective heat conductivities were found to range between 0.4 and 1.5 W/(m K). These values are in good agreement with previous data obtained with the use of laser flash and insulated hot wire methods. The precision of the new technique was also found to be in the range of this other techniques.

Crystal Structure Defects and Composition of Micas from Lamproites: Mössbauer and Infrared Data

Elena Lepekhina (selena@aa2074.spb.edu), Miriam Babushkina (msb@mb2171.spb.edu), Larisa Nikitina (nikita@ad.iggp.ras.spb.ru), Nikita Ovchinnikiv (nikita@ad.iggp.ras.spb.ru) & Kirill Lokhov

Institute of Precambrian Geology and Geochronology, Russian Academy of Science, Makarova emb. 2, St-Petersburg, 199034, Russia

Micas from the mantle rocks: the sanidine lamproites of transitional type (Por`ya Bay, 1720±8 m.y) and olivine lamproites (Kostomuksha, 1230±5 m.y.) the Baltic shield are investigated by methods of the electron microprobe analysis, Mössbauer and Infrared spectroscopy [1]. Phlogopites from sanidine lamproites can be related to phlogopite-biotite isomorphous series and contain 1-4 wt.% TiO₂, 3-13 wt.% FeO, 17-25 wt.% MgO, 1-4 wt.% Fe₂O₃, 12-15 wt.% Al₂O₃, 41-43 wt.% SiO₂. Phlogopites from olivine lamproites are the members of phlogopite-tetraferriphlolopite isomorphous series. They are depleted in Al₂O₃ (3-12 wt.%) and enriched in TiO₂ (3-6 wt.%). The contents of the basic oxides are 39-44 wt.% SiO₂, 3-5 wt.% FeO, 3-12 wt.% Fe₂O₃, 21-26 wt.% MgO. The degree of oxidation state of iron in micas from olivine lamproites (Fe³⁺ /Fe²⁺ = 0.57-2.00) and lamproites of transitional type (Fe³⁺ /Fe²⁺ = 0.21-0.36) is much greater than one in micas from core rocks. In micas of phlogopite-tetraferripholopite isomorphous series Fe³⁺ is distributed between tetrahedral (IV) and octahedral (VI) positions in the relation Fe³⁺_IV/Fe³⁺_VI = 0.60-2.29. At deficiency Si and Al (< 4.0 f.u.) the free positions IV are filled by both cations Fe³⁺ and Ti⁴⁺, even at the high contents Fe³⁺, sufficient for occupation all not filled tetrahedral positions. A part of cations Fe³⁺ and Ti occupy octahedral positions. In micas of phlogopite-biotite series Fe³⁺ occupies only octahedral position M2. Tetrahedral positions which have been not populated Si⁴⁺ and Al³⁺, are filled by Ti⁴⁺. The character of Fe²⁺ distribution on octahedral positions M1 and M2 in phenocrysts and groundmass plates is various. In phenocrysts disordering distribution of Fe²⁺ cations is observed. In groundmass plates Fe²⁺ is ordered in position M1. The significant quantity of vacancies in interlayer position and in octahedral layer and presence of molecular water in various energy positions is established. In micas a quantity of H₂O, chemically active gases CO₂, N₂ (up to 200 ccSTP/g) and inert gases (Ar) is higher in comparison with micas from core rocks (Nikitina et al., 1998). So, the micas from lamproites are characterized by a high degree of crystal structure defects shown in a high degree of cations disordering, in significant quantity of vacancies in octahedral layer and interlayer position. The vacancies, apparently, were used as effective structural traps for fluid components.

Nikitina LP, Levskiy LK, Beliatsky BV, Juravlev BA, Lepekhina EN, Antonov AV, Petrology, 3, 40-61, (1999).