DOCSLIB.ORG

An Experimental Study of Tremolite Dissolution Rates As a Function of Ph and Temperature: Implications for Tremolite Toxicity and Its Use in Carbon Storage

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Experimental Study of Tremolite Dissolution Rates As a Function of Ph and Temperature: Implications for Tremolite Toxicity and Its Use in Carbon Storage Mineralogical Magazine, November 2014, Vol. 78(6), pp. 1449–1464 OPEN ACCESS An experimental study of tremolite dissolution rates as a function of pH and temperature: Implications for tremolite toxicity and its use in carbon storage 1,} 1 1,2, TAMARA DIEDRICH ,JACQUES SCHOTT AND ERIC H. OELKERS * 1 GET-Universite´ de Toulouse-CNRS-IRD-OMP, 14 Avenue Edouard Belin, 31400 Toulouse, France 2 Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK [Received 12 August 2014; Accepted 9 November 2014; Associate Editor: T. Stawski] ABSTRACT Steady-state tremolite dissolution rates, at far-from-equilibrium conditions, were measured as a function of aqueous silica and magnesium activity, pH from 1.9 to 6.7, and temperature from 25 to 150ºC. Calcium is released from tremolite faster than either Mg or Si throughout most of the experiments even after these latter elements attained steady-state release rates. The preferential removal of Ca releases fine Mg-Si rich needle-like fibres from the tremolite, probably promoting its toxicity. In contrast, Mg was released in stoichiometric or near to stoichiometric proportion to Si once steady-state was attained. Measured steady-state tremolite dissolution rates based on Si release can be described using 8 8 9 9 > 2 1=8> > > a þ > > > > H > > rþ ¼ :>AA: ; ;> expðEA=RTÞ aMg2þ where r+ signifies the BET surface area-normalized forward tremolite steady-state dissolution rate, AA À3 À2 À1 refers to a pre-exponential factor = 6610 mol cm s , EA designates an activation energy equal to À1 80 kJ mol , R represents the gas constant, T denotes absolute temperature, and ai refers to the activity of the subscripted aqueous species. This rate expression is consistent with tremolite dissolution rates at acidic pH being controlled by the detachment of partially liberated silica tetrahedra formed from the exchange of Mg2+ for two protons near the mineral surface after the near-surface Ca has been removed. Nevertheless, Mg release rates from tremolite are ~3 orders of magnitude slower than those from forsterite and enstatite suggesting that tremolite carbonation will be far less efficient than the carbonation of these other Mg-silicate minerals. KEYWORDS: tremolite, dissolution rates, biodurability, mineral carbonation. Introduction the divalent metal silicates, including studies of THIS work is part of a systematic study aimed at the dissolution rates of forsterite (Murphy and the characterization of Mg-silicate mineral Helgeson, 1987, 1989; Wogelius and Walther, dissolution rates. A significant number of past 1991, 1992; Pokrovsky and Schott, 2000; Rosso studies have focused on the dissolution rates of This paper is published as part of a special issue in * E-mail: [email protected] Mineralogical Magazine, Vol. 78(6), 2014 entitled } Present address: Barr Consulting, Duluth MN, USA ‘Mineral–fluid interactions: scaling, surface reactivity DOI: 10.1180/minmag.2014.078.6.12 and natural systems’. # 2014 The Mineralogical Society Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/78/6/1449/2923053/gsminmag_78_6_12_die_OA.pdf by guest on 24 September 2021 TAMARA DIEDRICH ET AL. and Rimstidt, 2000; Oelkers, 2001b; Golubev et 4 9 in aqueous solutions containing HCl, al., 2005; Olsen and Rimstidt, 2008; Prigiobbe et KHCO3,H3BO3 and KOH measured in fluidized al. 2009; Daval et al., 2011a; King et al., 2014), bed reactors. Measured rates decrease slightly with enstatite (Schott et al., 1981; Oelkers and Schott, increasing pH to at least pH 9. In addition, both of 2001), diopside (Petit et al., 1987; Knauss et al., these experimental studies observed a preferential 1993; Brantley and Chen, 1995; Chen and release of Mg over Si during the early stages of Brantley, 1998; Golubev et al., 2005; Golubev experiments performed at acidic conditions prior and Pokrovsky, 2006; Dixit and Carroll, 2007; to attainment of stoichiometric steady-state Daval et al., 2011b, 2013) and talc (Lin and dissolution. This behaviour and similar observa- Clemency, 1981; Jurinski and Rimstidt, 2001; tions on other divalent metal silicates reported by Saldi et al., 2007). Oelkers et al. (2009) were attributed to a relatively The motivation for this study is several fold: rapid exchange reaction between H+ and Mg2+ on (1) The dissolution rates of Ca- and Mg-bearing the mineral surfaces. Similarly, Schott et al. silicates, such as tremolite, are of particular (1981) reported that Ca was preferentially released interest as they are potential sources of the compared to both Mg and Si during tremolite divalent metals required for the mineralogical dissolution at acid conditions. Mast and Drever storage of CO2 (cf. Oelkers and Schott, 2005; (1987) performed additional tremolite dissolution Ha¨nchen et al., 2008; Oelkers and Cole, 2008; experiments at pH 4 and 7 as a function of Oelkers et al., 2008a; King et al., 2010; Ryu et aqueous oxalate concentrations. In contrast to the al., 2011; Saldi et al., 2012; Gislason and Oelkers, effect of the presence of aqueous organic species 2014). on Al-silicate minerals (cf. Oelkers and Schott, (2) Exposure to tremolite is widely recognized 1998), no effect of the presence of aqueous oxalate as a cause of asbestos-related diseases (Churg, was observed for oxalate concentrations À3 1988; Case, 1991; Davis et al., 1991; Robledo and 410 M. The present study expands upon this Mossman, 1999; Roggli et al., 2002; Gunter et al., past work by determining tremolite steady-state 2007; Pugnaloni et al., 2013). A particle’s ability dissolution rates over a wide range of pH at to resist dissolution once submerged in lung fluid temperatures between 25 and 150ºC and by (i.e. its biodurability) may be a critical determinant establishing an equation to describe these rates in its toxicity (Addison and McConnell, 2008). over a variety of environmental conditions. This connection has motivated several previous studies aimed at quantifying tremolite biodur- Theoretical background ability (Oze and Solt, 2010; Rozalen et al., 2013). (3) The dissolution rates of the Mg silicates The standard state adopted in this study is that of appear to exhibit a systematic behaviour as a unit activity for pure minerals and H2O at any function of aqueous solution pH and composition temperature and pressure. For aqueous species (Schott et al., 2009). It is anticipated that this other than H2O, the standard state is unit activity study will provide further insight into this of the species in a hypothetical 1 molal solution systematic behavior of these minerals. referenced to infinite dilution at any temperature The goal of this study is to expand our and pressure. Tremolite dissolution can be knowledge of tremolite dissolution kinetics at described according to: acid to neutral pH. Thus tremolite dissolution + Ca2Mg5Si8O22(OH)2 + 14H > rates have been measured at 25 to 150ºC, and 2Ca2+ 5Mg2+ + 8SiO (aq) + 8H O (1) 1.9 < pH < 6.7 as a function of aqueous fluid 2 2 concentration at far-from-equilibrium conditions. Note that SiO2(aq) in reaction 1 represents the The results of this study illuminate the durability H4SiO4 neutral aqueous species rather than total of tremolite at conditions relevant to mineral dissolved Si. Taking account of the standard state, carbonation and human health. the law of mass action for reaction 1 can be To date there have been relatively few studies written of the dissolution rates of tremolite reported in the 2 5 8 À14 Ktremolite ¼ a 2þ a 2þ a a þ ð2Þ literature. Schott et al. (1981) reported the Ca Mg SiO2ðaqÞ H dissolution rates of tremolite at 22ºC at 1 4 pH 4 6 in aqueous HCl solutions measured in batch where Ktremolite stands for the equilibrium reactors. Mast and Drever (1987) reported the constant of reaction 1, and ai represents the dissolution rates of tremolite at 22ºC and 2 4 pH activity of the subscripted aqueous species. The 1450 Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/78/6/1449/2923053/gsminmag_78_6_12_die_OA.pdf by guest on 24 September 2021 EXPERIMENTAL STUDY OF TREMOLITE DISSOLUTION RATES chemical affinity (A)forreaction1canbe Steady-state forward tremolite dissolution rates expressed as in this study are quantified using the multi-oxide 8 9 2 5 8 silicate dissolution model of Oelkers (2001a). >a 2þ a 2þ a > > Ca Mg SiO2ðaqÞ> Within this model, dissolution proceeds via the A ¼ RT ln:> ;> ð3Þ 14 sequential breaking of metalÀoxygen bonds until KtremoliteaHþ the mineral structure is destroyed. The tremolite where R designates the gas constant, and T structure consists of CaÀO and MgÀO bonds in represents absolute temperature. When the fluid 8-fold and 6-fold coordination, respectively, and is undersaturated with respect to tremolite, A is tetrahedral SiÀO bonds (Hawthorne and Oberti, negative, and when the fluid is supersaturated, A 2007). Silicon tetrahedra form double chains is positive. All thermodynamic calculations layered between strips of edge-sharing octahedra. reported in the present study were performed In accord with Oelkers (2001a) and consistent using the PHREEQC 2.6 computer code with the results reported below, the relative rate of (Parkhurst and Appelo, 1999) together with its breaking these bonds are CaÀO>MgÀO> llnl database (Johnson et al., 2000). It is assumed SiÀO. This conclusion is consistent with the in all thermodynamic calculations that the solid observations that Mg and Ca are initially released used in the dissolution experiments was pure more rapidly than Si from divalent metal silicates stoichiometric tremolite. Although surface (e.g. Luce et al., 1972; Lin and Clemency, 1981; complexation theory suggests that the activities Schott et al., 1981; Berner and Schott, 1982; Petit of charged particles on charged surfaces may et al., 1987; Oelkers and Schott, 2001; Oelkers et differ somewhat from unity (Davis and Kent, al., 2009). Such observations suggest that the 1990), the activities of species at the tremolite tremolite dissolution mechanism is initiated by surface are assumed to be equal to their mole the relatively rapid removal of Ca atoms and Mg fraction.
Load more

Recommended publications
  • Yellowish Green Diopside and Tremolite from Merelani, Tanzania
    YELLOWISH GREEN DIOPSIDE AND TREMOLITE FROM MERELANI, TANZANIA Eric A. Fritz, Brendan M. Laurs, Robert T. Downs, and Gelu Costin tion (typical of diopside, which is a pyroxene) shown by other crystals in the parcels. Four similar-appearing yellowish green samples Mr. Ulatowski loaned one example of both types of from Block D at Merelani, Tanzania, were identified crystals to GIA for examination (figure 1), and we also as diopside and tremolite. The gems are identical in color, but their standard gemological properties are typical for calcic pyroxene and amphibole. The identification of the diopside was made with Raman Figure 1. These yellowish green crystals were recov- spectroscopy, while single-crystal X-ray diffraction ered from Block D at Merelani in the latter part of and electron-microprobe analyses were used to 2005. A blocky morphology is shown by the diopside confirm the amphibole species as tremolite. crystal (1.6 cm tall; left and bottom), whereas the Absorption spectroscopy (in the visible–mid-infrared tremolite crystal has a flattened, diamond-shaped range) revealed that the two gem materials are col- cross-section. Photos by Robert Weldon. ored by V3+, Cr3+, or both. t the 2006 Tucson gem shows, Steve Ulatowski A showed one of the authors (BML) some yellowish green crystals that he purchased as diopside while on buy- ing trips to Tanzania in August and November 2005. The material was reportedly produced during this time period from Block D at Merelani, in the same area that yielded some large tsavorite gem rough (see Laurs, 2006). Mr. Ula- towski obtained 1,200 grams of the green crystals, mostly as broken pieces ranging from 0.1 to 50 g (typically 1–5 g).
    [Show full text]
  • X-Ray Structure Refinements of Tremolite at 140 and 295 K: Crystal Chemistry and Petrologic Implications
    American Mineralogist, Volume 81, pages 1117-1125,1996 X-ray structure refinements of tremolite at 140 and 295 K: Crystal chemistry and petrologic implications HEXIONG YANG1.. ANDBERNARD W. EVANS2 'Department of Geological Sciences. Campus Box 250, University of Colorado, Boulder, Colorado 80309-0250, U.S.A. 2Department of Geological Sciences, Box 351310, University of Washington, Seattle, Washington 98195-1310, U.S.A. ABSTRACT A near-end-member natural tremolite, N!lo.o,Ca1.97M~.9sFeo.Q3Alo.oISis.oo022(OH)2'was studied by single-crystal X-ray diffraction at 140 and 295 K to seek a possible crystal- chemical explanation for the typically low CaI~ M ratios, relative to the ideal ratio of 2/5, observed in both natural and synthetic tremolite samples. Difference-Fourier maps re- vealed the presence of a residual electron density close to the M4 site along the diad axis toward the octahedral strip. Structure refinements indicated that the M4 and M4' sites are occupied by Ca + Na and M(Fe + Mg), respectively. In comparison with the configuration of the M2 coordination polyhedron in diopside, the degree of distortion and the volume of the M4 coordination polyhedron in tremolite are relatively large and the M4 cation is slightly underbonded. These two factors contribute to an energetic drive toward M-en- riched tremolite. The average unit-cell volume of 906.6(2) A3 determined at 295 K for nearly pure tremolite in this study suggests an end-member reference-state volume for tremolite of907 A3. This indicates that cell volumes of synthetic tremolite of 904.2(4) A3 reflect 8-10% cummingtonite solid solution, as previous authors have claimed.
    [Show full text]
  • Tungsten Minerals and Deposits
    DEPARTMENT OF THE INTERIOR FRANKLIN K. LANE, Secretary UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Bulletin 652 4"^ TUNGSTEN MINERALS AND DEPOSITS BY FRANK L. HESS WASHINGTON GOVERNMENT PRINTING OFFICE 1917 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 25 CENTS PER COPY CONTENTS. Page. Introduction.............................................................. , 7 Inquiries concerning tungsten......................................... 7 Survey publications on tungsten........................................ 7 Scope of this report.................................................... 9 Technical terms...................................................... 9 Tungsten................................................................. H Characteristics and properties........................................... n Uses................................................................. 15 Forms in which tungsten is found...................................... 18 Tungsten minerals........................................................ 19 Chemical and physical features......................................... 19 The wolframites...................................................... 21 Composition...................................................... 21 Ferberite......................................................... 22 Physical features.............................................. 22 Minerals of similar appearance.................................
    [Show full text]
  • The Effect of Grinding on Tremolite Asbestos and Anthophyllite Asbestos
    minerals Article The Effect of Grinding on Tremolite Asbestos and Anthophyllite Asbestos Andrea Bloise 1,* ID , Robert Kusiorowski 2 ID and Alessandro F. Gualtieri 3 1 Department of Biology, Ecology and Earth Sciences, University of Calabria, via Pietro Bucci, I-87036 Rende, CS, Italy 2 Institute of Ceramics and Building Materials, Refractory Materials Division in Gliwice, ul. Toszecka 99, 44-100 Gliwice, Poland; [email protected] 3 Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, I-41125 Modena, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-0984-493588 Received: 4 June 2018; Accepted: 25 June 2018; Published: 28 June 2018 Abstract: The six commercial asbestos minerals (chrysotile, fibrous actinolite, crocidolite, amosite, fibrous tremolite, and fibrous anthophyllite) are classified by the IARC as carcinogenic to humans. There are currently several lines of research dealing with the inertisation of asbestos minerals among which the dry grinding process has received considerable interest. The effects of dry grinding on tremolite asbestos and anthophyllite asbestos in eccentric vibration mills have not yet been investigated. Along the research line of the mechanical treatment of asbestos, the aim of this study was to evaluate the effects of dry grinding in eccentric vibration mills on the structure, temperature stability, and fibre dimensions of tremolite asbestos from Val d’Ala, (Italy) and UICC standard anthophyllite asbestos from Paakkila mine (Finland) by varying the grinding time (30 s, 5 min, and 10 min). After grinding for 30 s to 10 min, tremolite asbestos and anthophyllite asbestos showed a decrease in dehydroxylation and breakdown temperatures due to the increase in lattice strain and the decrease in crystallinity.
    [Show full text]
  • Vermiculite Is Not Asbestos
    VERMICULITE IS NOT ASBESTOS There are no real causes for concern about health risks from vermiculite: a review of the mineralogy of vermiculite and its fundamental differences to asbestos explains why. John Addison Addison-Lynch, Edingburgh February 1994 SUMMARY • Vermiculite is a sheet silicate mineral that is found as flaky crystals; it is not a fibrous mineral like asbestos. Fibres of vermiculite can be formed by breakage of the flakes or by curling of the edges of the flakes. Such mineral fibres do not constitute asbestos, and fibrous shape does not, by itself, mean that they will behave like asbestos. • Vermiculite dusts, including these fibrous fragment forms, have demonstrated very few if any health effects, other than those that could be expected from any low toxicity silicate. Unlike asbestos, vermiculite has shown very few ill-effects in experimental testing with animals. Chemical testing suggests that it may not stay long enough in the lung to do serious damage. • All vermiculite ores contain a range of other minerals that were formed along with the vermiculite in the rock. Vermiculite ores from some sources were even found to contain asbestos minerals but asbestos is not intrinsic to vermiculite and only a few ore bodies have been found to contain more than tiny trace amounts. Nevertheless serious public concern was generated because of the known occurrences of asbestos in vermiculite deposits such as those in Montana that were closed some years ago • Asbestos is the name given to a number of naturally occurring fibrous silicate minerals that have been exploited for their useful properties such as thermal insulation, chemical and thermal stability, and high tensile strength.
    [Show full text]
  • Minerals Found in Michigan Listed by County
    Michigan Minerals Listed by Mineral Name Based on MI DEQ GSD Bulletin 6 “Mineralogy of Michigan” Actinolite, Dickinson, Gogebic, Gratiot, and Anthonyite, Houghton County Marquette counties Anthophyllite, Dickinson, and Marquette counties Aegirinaugite, Marquette County Antigorite, Dickinson, and Marquette counties Aegirine, Marquette County Apatite, Baraga, Dickinson, Houghton, Iron, Albite, Dickinson, Gratiot, Houghton, Keweenaw, Kalkaska, Keweenaw, Marquette, and Monroe and Marquette counties counties Algodonite, Baraga, Houghton, Keweenaw, and Aphrosiderite, Gogebic, Iron, and Marquette Ontonagon counties counties Allanite, Gogebic, Iron, and Marquette counties Apophyllite, Houghton, and Keweenaw counties Almandite, Dickinson, Keweenaw, and Marquette Aragonite, Gogebic, Iron, Jackson, Marquette, and counties Monroe counties Alunite, Iron County Arsenopyrite, Marquette, and Menominee counties Analcite, Houghton, Keweenaw, and Ontonagon counties Atacamite, Houghton, Keweenaw, and Ontonagon counties Anatase, Gratiot, Houghton, Keweenaw, Marquette, and Ontonagon counties Augite, Dickinson, Genesee, Gratiot, Houghton, Iron, Keweenaw, Marquette, and Ontonagon counties Andalusite, Iron, and Marquette counties Awarurite, Marquette County Andesine, Keweenaw County Axinite, Gogebic, and Marquette counties Andradite, Dickinson County Azurite, Dickinson, Keweenaw, Marquette, and Anglesite, Marquette County Ontonagon counties Anhydrite, Bay, Berrien, Gratiot, Houghton, Babingtonite, Keweenaw County Isabella, Kalamazoo, Kent, Keweenaw, Macomb, Manistee,
    [Show full text]
  • Management of Asbestos in Vermiculite Insulation
    Management of Asbestos in Summary Asbestos Fibres Zonolite® - Vermiculite Insulation ‘Vermiculite’ insulation presents a small but identifiable risk to long term health. When it is identified in a building, it should be verified and isolated from the occupied spaces of the building. Personnel required to enter the space containing the vermiculite insulation must wear protective INFORMATION FOR PWS STAFF AND FACILITY USERS clothing and approved respiratory apparatus. For additional Information, contact Technical Support Services, Asset Management Division, Public Works and Services. ASBESTOS Minerals Containing The Issue: Purpose Asbestos Fibres Some vermiculite insulation This document is to inform PWS staff about vermiculite may contain amphibole loose fill thermal insulation and provide operational safety asbestos bres. These guidelines for use when vermiculite is present in a building. products can cause health Loose fill insulation is usually installed in attic spaces above risks if disturbed during ceilings, and occasionally in the sealed compartments What is Vermiculite? maintenance, renovation or between studs in wood frame construction or as fill in cement block construction. Vermiculite was also used in demolition. However, there Vermiculite is a naturally occurring fireproofing materials, and as a lightweight aggregate in is currently no evidence of “mica-like” mineral that was mined construction materials. risk to your health if the and processed into attic insulation insulation is sealed starting in the 1920’s and ending in Vermiculite is a shiny mineral, similar to mica, which pops (encapsulated) behind the early 1990’s. When heated to like corn when heated. The puffy product, as light as cork, wallboards and oorboards, around 1000 degrees C, it pops (or was once a popular form of building insulation and is still an isolated in an attic, or puffs up) which creates pockets of ingredient in potting soil.
    [Show full text]
  • Comparison of Calcite + Dolomite Thermometry and Carbonate +
    American Mineralogist, Volume 80, pages 131-143, 1995 Comparison of calcite + dolomite thermometry and carbonate + silicate equilibria: Constraints on the conditions of metamorphism of the Llano uplift, central Texas, U.S.A. CHERITH M. R. LETARGO,WILLIAM M. LAMB* Department of Geology and Geophysics, Texas A & M University, College Station, Texas 77843, U.S.A. JONG-SIM PARK** Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, Wisconsin 53706, U.S.A. ABSTRACT Temperatures based on the composition of calcite coexisting with dolomite (calcite + dolomite thermometry) range from 475 to 600°C for 63 marbles from the Llano uplift of central Texas. The highest temperatures, -600°C, were obtained by carefully reintegrating calcite containing exsolved lamellae of dolomite. In some cases, these high temperatures were determined for marbles that contain an isobarically invariant assemblage consisting of calcite + dolomite + tremolite + diopside + forsterite. At a pressure of 3 kbar, these five minerals are stable at 630 OCand Xco, = 0.62. In contrast, relatively low calcite + dolomite temperatures of 475-480 °Cwere obtained for marbles containing the assemblage calcite + dolomite + tremolite + talc. This talc-bearing assemblage is stable at ~475 OC, depending on fluid composition, at a pressure of 3 kbar. Additional isobarically univariant equilibria are stable at intermediate temperatures (generally between 535 and 630 0q, and these are also generally consistent with results obtained from calcite + dolomite thermom-
    [Show full text]
  • Thermal Stability and Oxidation Processes in Amphiboles on the Tremolite – Ferro-Actinolite Join Studied by Raman Spectroscopy
    Thermal stability and oxidation processes in amphiboles on the tremolite – ferro-actinolite join studied by Raman spectroscopy Bachelor Thesis Mineralogisch-Petrographisches Institut Universität Hamburg Constanze Rösche Supervised by: Prof. Dr. Boriana Mihailova Prof. Dr. Jochen Schlüter Date of submission: 01.11.2018 Thermal stability and oxidation processes in amphiboles on the tremolite – ferro-actinolite join studied by Raman spectroscopy Abstract In this study an actinolite, the intermediate member of the tremolite – ferro-actinolite series, 2+ ideally Ca2(Mg,Fe )Si8O22(OH)2, has been examined regarding its thermal stability and oxidation behavior by conducting in situ Raman spectroscopic experiments. Spectra have been recorded in the ranges from 15-1215 cm-1 and 3370-3770 cm-1 at temperatures from 100-870 K in nitrogen atmosphere and at temperatures from room temperature to 1300 K in air. The heat treatment in nitrogen atmosphere did not cause any irreversible changes while on heating in air divalent iron is oxidized. At 1100 K hydrogen cations bonded to the oxygen anion at the W-site of the amphibole structure and electrons associated to Fe2+ at the octahedral sites start to delocalize but remain inside the crystal matrix. The delocalization is completed at 1300 K. When cooling to room temperature the initial state is only partly recovered. Therefore some hydrogen and electrons must have been ejected from the crystal. Changes in peak positions and intensities, new appearing and disappearing peaks indicate that some divalent iron has been oxidized to trivalent iron. In the final spectrum the peaks related to the chemical configurations M(1)M(1)M(3)Fe2+MgMg–A□ and M(1)M(1)M(3)Fe2+MgMg–A-site appear strongly shifted to lower wavenumbers with a decreased intensity, which indicates that the configurations have changed to M(1)M(1)M(3)Fe3+MgMg–A□ and M(1)M(1)M(3)Fe3+MgMg–A-site.
    [Show full text]
  • Tremolite–Calcite Veins in the Footwall of the Simplon Fault, Antigorio Valley, Lepontine Alps (Italy)
    Swiss J Geosci (2011) 104:355–365 DOI 10.1007/s00015-011-0074-0 Tremolite–calcite veins in the footwall of the Simplon Fault, Antigorio Valley, Lepontine Alps (Italy) Vito Meggiolaro • Michele Sapigni • Anna Maria Fioretti Received: 23 February 2011 / Accepted: 19 August 2011 / Published online: 19 October 2011 Ó Swiss Geological Society 2011 Abstract The lowermost units of the nappe pile of the 450 and 490°C and minimum pressure of 2–3 kbar. Such Lepontine Alps crop out in the Antigorio valley in the foot- temperature conditions occurred in this footwall region of wall of the Simplon Fault. The whole orthogneiss section of the Simplon Fault Zone around 15 Ma, during exhumation the Antigorio Unit is exposed on both sides of the valley, and cooling of the nappe pile and a transition to brittle sandwiched between the Mesozoic metasedimentary behaviour. Aqueous, silica-rich fluids concentrated along sequences of the Baceno unit below and the Te`ggiolo unit fractures, forming tremolite–calcite veins in the dolomite above. The petrography and mineral composition of tremo- marbles and quartz veins in the orthogneiss. lite–calcite veins occurring in dolomite marble in both metasedimentary sequences were investigated. Tremolite– Keywords Tremolite Á Vein Á Simplon Á Antigorio valley calcite (with lesser talc and minor phlogopite) veins have rhythmic banded texture. Banding is due to cyclic differ- ences in modal abundances and fabric of tremolite and 1 Introduction calcite. These veins are very similar to those occurring in dolomite rafts within the Bergell granite and it is inferred that The Lepontine dome is one of the best studied areas of the they formed by the same ‘‘fracture-reaction-seal’’ mecha- central Penninic Alps, and its structural and metamorphic nism.
    [Show full text]
  • Identification Tables for Common Minerals in Thin Section
    Identification Tables for Common Minerals in Thin Section These tables provide a concise summary of the properties of a range of common minerals. Within the tables, minerals are arranged by colour so as to help with identification. If a mineral commonly has a range of colours, it will appear once for each colour. To identify an unknown mineral, start by answering the following questions: (1) What colour is the mineral? (2) What is the relief of the mineral? (3) Do you think you are looking at an igneous, metamorphic or sedimentary rock? Go to the chart, and scan the properties. Within each colour group, minerals are arranged in order of increasing refractive index (which more or less corresponds to relief). This should at once limit you to only a few minerals. By looking at the chart, see which properties might help you distinguish between the possibilities. Then, look at the mineral again, and check these further details. Notes: (i) Name: names listed here may be strict mineral names (e.g., andalusite), or group names (e.g., chlorite), or distinctive variety names (e.g., titanian augite). These tables contain a personal selection of some of the more common minerals. Remember that there are nearly 4000 minerals, although 95% of these are rare or very rare. The minerals in here probably make up 95% of medium and coarse-grained rocks in the crust. (ii) IMS: this gives a simple assessment of whether the mineral is common in igneous (I), metamorphic (M) or sedimentary (S) rocks. These are not infallible guides - in particular many igneous and metamorphic minerals can occur occasionally in sediments.
    [Show full text]
  • The Tremolite-Actinolite-Ferro–Actinolite Series
    American Mineralogist, Volume 85, pages 1239–1254, 2000 The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities JENNIFER R. VERKOUTEREN1,* AND ANN G. WYLIE2 1Chemical Sciences and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, U.S.A. 2Laboratory for Mineral Deposits Research, Department of Geology, University of Maryland, College Park, Maryland 20742, U.S.A. ABSTRACT Unit-cell parameters, optical properties, and chemical compositions have been measured for 103 samples in the tremolite-actinolite-ferro-actinolite series. The average values of the non-essential constituents are: TAl = 0.10(11), CAl = 0.06(6), B(Fe, Mn, Mg) = 0.09(7), BNa = 0.04(5), ANa = 0.09(9), and Cr, Ti, and K ≅ 0. Asbestiform actinolite samples have lower Al contents than massive or “byssolitic” actinolite samples. Unit-cell parameters for end members tremolite and ferro-actino- lite based on regressions of the data are: a = 9.841 ± 0.003 Å, 10.021 ± 0.011 Å; b = 18.055 ± 0.004 Å, 18.353 ± 0.018 Å; c = 5.278 ± 0.001 Å, 5.315 ± 0.003 Å; and cell volume = 906.6 ± 0.5 Å3, 944 ± 2 Å3. The changes in a, b, and cell volume with ferro-actinolite substitution are modeled with quadratic functions, and the change in c with ferro-actinolite substitution is modeled with a linear function. There is a positive correlation between c and Al that results in a discrimination between asbestiform and massive or “byssolitic” habits for c and for the refractive indices.
    [Show full text]