American Mineralogist, Volume 93, pages 1349-1355, 2008

Crystal chemical and structural characterization of fibrous tremolite from Susa Valley,Italy, with comments on potential harmful effects on human health

PAOLO BALLIRANO,1,2,* GIOVANNI B. ANDREOZZI,1,3 AND GIROLAMO BELARDI2

'Dipartimento di Scienze della Terra, Sapienza Universita di Roma, P.leA. Mora, 5, 1-00185 Rome, Italy2CNR-IGAG, Istituto di Geologia Ambienta1e e Geoingegneria, Sede eli Roma, Via Bo1ogno1a 7,1-00138 Rome, Italy

3CNR-IGG, Istituto di Geoscienze e Georisorse, Sede eli Roma, P.le A. Mora, 5, 1-00185 Rome, Italy

ABSTRACT

This study is part of a broad research project devoted to the "amphibole fibers environmental prob-lem" as related to the proposed excavation of the Susa Valley railway tunnel. In this locality, tunnelexcavations are planned through metamorphic formations containing amphibole asbestos minerals, andthis may give rise to worker health and public environmental issues. The Susa Valley tremolite showsa marked fibrous character, a small reduction of fiber size under grinding, and a consistent increaseof the surface area. From the toxicological point of view, such tremolite fibers have been shown tobe very effective in the generation of reactive oxygen species. They exhibit a very high cellular re-activity as a consequence of their morphology, structure, and crystal chemistry. Results of combinedelectron microprobe analysis, Mossbauer spectroscopy, and parallel-beam X-ray powder diffractionare reported for fibrous tremolite from a serpentine-schist from the "Unita Oceanica della Bassa Valdi Susa" collected near Condove, Susa Valley, Italy. Data indicate that Fe2+(84% of Fe tot) is located atboth the (Ml + M3) and M2 sites and that Fe3+is at M2, in an approximate 3:2: 1 ratio, respectively.No evidence of a split M4 site has been observed. The presence of Ml+M3Fe2+is confirmed by FTIRspectroscopy to be distributed 70% at Ml and 30% at M3. Both the composition (Ca19SKoOlNaoosbol(VIAloOlFd+02Fe5+11Mg484Mllo02booSi8oo0nC0H196Fo03CloOlbooand the cell volume 907.37(1) A3 ofthe fibers are close to those expected for end-member (CalMg = 2/5) tremolite.

Keywords: Fibrous tremolite, amphibole crystal chemistry, Mossbauer spectroscopy, Rietveldmethod, electron microprobe analysis, Susa Valley, Italy, Trans European Network

INTRODUCTION

In the near future, nnmerous construction projects are likely tobe carried out in northern Italy, all belonging to corridor 5 of theTEN (Trans European Network). In particular, some high-speedrailway lines such as Turin-Lyon and Genoa-Milan will involvetunnel excavations occurring in metamorphic formations, suchas serpentinites, in which zones containing asbestos mineralsmay be found. These excavations give rise to worker health andpublic environmental issues (Piolatto et al. 1990; Astolfi et al.1991). This contribution is a part of a broad research programdevoted to the complete definition of the "amphibole fibersenvironmental problem" related to the proposed excavationof the Susa Valley railway tunnel. Its goal is to provide up-to-date, clear information to both policy-makers and stakeholdersto minimize hnman exposure to potentially harmful materials.When inhaled, asbestos fibers may give rise to either non-tu-mor diseases or malignant tumors in the lungs (Martuzzi et al.1999) and pleura (Mastrantonio et al. 2002). Particular attentionshould be paid to the effects of asbestos on the rise of pleuralmesothelioma (Bignon et al. 1996). The main features of suchtumors are particularly long latency, occurrence related to indi-

* E-mail: paolo.ballirano@uniromal.it

0003-004X/08/0809-1349$05.00/DOI: 10.2138/am.2008.2869 1349

vidual susceptibility, a difficult diagnosis, a previous exposureonly to asbestos of the amphibole group (Constantopoulos et al.1987), and most of all, the capability of appearing even after theinhalation of an extremely low asbestos concentration known astriggering dose (U.S. National Research Council 1985; Piolatto1996). The mechanism through which asbestos fibers may giverise to cancer is not yet completely clear. Many authors agreein attributing the biological activity of the fibers to numerousfactors: dimension (Stanton et al. 1981), chemical composition(Fubini 1996; Gilmour et al. 1997), surface properties (Fubini1993), solubility, and bio persistence (Liu et al. 2000). The diam-eter and length influence the mechanism of capture and rejectionof the fibers. The results of in vitro and in vivo studies show thatthe longer and thiuner fibers are the more dangerous. In fact, thefibers with diameters less than 3 urn and lengths more than 20urn are partially phagocyted by the alveolar macrophages, withthe consequent release of chemical species capable of reactingwith the oxygen, causing damage to DNA due to oxidation andmodification of the cell's surface. Chemical composition mayalso contribute to the occurrence of cancer through the presenceof iron that may give rise to species capable of reacting with theoxygen, causing the already-mentioned damage. Recent Italianlegislation (directives 67/548/CEE and 97/69/CEE) takes into ac-count the above concepts in labeling and classifying carcinogenic

1350 BALLIRANO ET AL.: CRYSTAL CHEMISTRY OF FIBROUS TREMOLITE, SUSA VALLEY, ITALY

agents, focusing particularly on chemical composition (alkalineand terrous-alkaline oxide concentrations), weighted mean diam-eter, length, and in vivo persistence (i.e., retention of the fibersin the lungs). Characterization of the asbestos minerals extractedduring the excavation phases of the construction projects, aswell as the development of analytical procedures for an effectivecharacterization of the asbestos hazard, are thus needed.

In the present study, fibrous tremolite from Susa Valley wasexamined. Tremolite is a monoclinic (C2/m), calcic amphibolewith a nominal formula of Ca2MgsSig022(OH)2' It is an end-member of the tremolite- ferro-actinolite series. The examinedhand specimen is composed of dolomite, tremolite, chlorite, andtalc. Tremolite veins contain minor calcite and iron oxides. Thespecimen comes from a serpentine schist of the "Unita Oceanicadella Bassa Val di Susa" of the so-called "Zona Piemontese"Units collected near Condove, Susa Valley. The serpentinitesfrom the Ligurian-Piedmontese formations are usually character-ized by a massive structure and fine-grained texture, althoughthey can occur in the form of highly laminated serpentine schistsand chlorite schists in tectonic contacts and fault zones. TheAlpine metamorphism within these rocks is found prevalently asa serpentinization process. The main mineralogical componentsare olivine (from which chrysotile asbestos minerals may haveformed after its metamorphic modification), clinopyroxene,orthopyroxene, plagioclase, and green spinel. Tremolite is foundin localized discontinuities (fault and/or fracture zones), parallelto the direction of movement (slickenside). The veins with thegreatest thickness, up to 5 em, are usually associated with faultmovements with extensional components. Tremolite may alsobe found in extension veins, with an orthogonal direction to themovement along fault fractures counected as the only kinematicallink to the extension veins. For a detailed geological outline ofthe Susa Valley in counection with the project of the Turin-Lyonhigh-speed railway, see Gattiglio and Sacchi (2006).

The present study is devoted to chemical, structural, andspectroscopic characterization, by combining electron micro-probe (EMP) analysis, parallel-beam X-ray powder diffraction(XRPD), s7Fe Mossbauer spectroscopy (MS), and Fourier-transform infrared (FT-IR) spectroscopy, of Susa Valley fibroustremolite. The aim is to provide detailed crystal-chemical insightsto be used to understand the relationships between mineralogicalcharacteristics and biological activity.

EXPERIMENTAL METHODS

Scanning electron microscopy and electron probemicroanalysis

Scauning electron microscopy (SEM) was performed usinga FEI Quanta 400 MK2 equipped with an EDAX Genesis EDSsystem. Images were obtained from a fragment of the handspecimen mounted on a sample stub and carbon coated. Analyti-cal conditions were: 30 kV accelerating voltage, 0.5 nA beamcurrent. Electron micrographs at low and high magnificationsare reported in Figure 1. Particle morphologies are restricted toacicular structures, fiber bundles, and rare, very small prismaticcrystals (Fig. la). Fibers are often curved and may reach centi-meter dimensions; width of individual fibrils is generally of theorder of 1 urn, but may be as small as 0.2 urn (Fig. 1b).

Bundles of fibers, selected using a binocular microscope,were embedded in epoxy and gently polished with diamond pasteto a y,,!lm finish. The composition oftremolite was determinedusing a Cameca SX50 electron microprobe equipped with fivewavelength-dispersive spectrometers using the following condi-tions: lOs counting time (peak), 5 s counting time (background),beam diameter 2 urn, excitation voltage 15 k.V, specimen current15 nA. The following standards were used: wollastonite (SiKaand CaKa), rutile (TiKa), corundum (AlKa), magnetite (FeKa),metallic manganese (MnKa), periclase (MgKa), orthoclase(KKa), jadeite (NaKa), fluorophlogopite (FKa), and sylvite(ClKa). Raw data were corrected online for drift, dead time, andbackground; matrix correction was performed with a standardZAF program. Of the total 30 analytical points, only 14 totaled>97 wt% and were therefore used for determining the sample av-erage chemical composition. For the remaining 16, the observedlow totals are attributed to the presence of voids between thesingle fibers arranged in bundles. However, even in these casesthe relative abundances of the elements gave crystal-chemicalformulae in excellent agreement with those selected. Table 1shows the averaged chemical composition, observed ranges,and crystal chemical formula normalized on the basis of 24(0+ F + Cl). Cations were assigned, following Hawthorne (1981),to the A, B, C, and T group sites, filled according to the orderrecommended by Leake et al. (1997).

57FE M6sSBAUER SPECTROSCOPY

The amphibole fibers were gently ground in an agate mortarwith acetone and mixed with a powdered acrylic resin to avoid(or reduce) preferred orientation. About 100 mg of sample wereavailable, and Fe total content was close to 1 wt%, so that theabsorber was within the limits for the thin absorber thicknessdescribed by Long et al. (1983). Data were collected at room

TABLE 1. Averaged chemical composition, ranges, and mean crystalchemical formula of the fibrous tremolite from SusaValley,analyzed by EPM (14 analytical points)

Oxides wt% Min.-Max. 5ites and Number of ionsvalues elements (0 + F + CI = 24)

5iO, 58.51 57.76-58.80 TTiO, 0.02 0-0.06 5i 8.003AI,03 0.05 0.02-0.14 2: 8.003FeOtot 1.17 0.65-1.41MnO 0.13 0.02-0.20 CMgO 23.74 23.27-24.55 v'AI 0.008CaO 13.29 12.61-13.92 Fe3+ 0.021Na,O 0.20 0.02-0.29 Fe2+ 0.113K,O 0.04 0-0.08 Mg 4.842F 0.07 0-0.16 Mn Om5CI 0.03 0-0.09 Ti 0.002H,O' 2.15 2: 5.001 = 62.111 e

99.40F,CI=O 0.03 B

Total 99.37 Ca 1.948Na 0.053

Fe,03t 0.20 0.12-0.25 K 0.007FeOt 0.99 0.55-1.18 2: 2.008 = 39.676 e

Ca/2:M 0.389

03OHFCI2:

1.9620.0300.009

2.001 = 16.119 e• Estimated from stoichiometry.t Partition according to Miissbauer spectroscopy.

BALLIRANO ET AL.: CRYSTAL CHEMISTRY OF FIBROUS TREMOLITE, SUSA VALLEY, ITALY

temperature, using a conventional spectrometer system operatedin constant acceleration mode with a 57COsource of nominalstrength of 50 mCi in rhodium matrix, and recorded with a mul-tichannel analyzer using 512 channels. The velocity range -1 0 to10 mmls was used to detect magnetic oxide impurities, in casethey were present. To have good statistics, more than 5 millionconnts per channel were collected. After velocity calibrationagainst a spectrum of high-purity a-iron foil (25 urn thick), theraw data were folded to 256 channels. The spectrum was fit usingthe Recoil 1.04 fitting program (Lagarec and Rancourt 1998).A first cycle was done fitting pure Lorentzian line shapes: dou-blet isomer shift (IS) and quadrupole splitting (QS), and sextetmagnetic field (H) were refined (as used in most papers fromthe literature) with excellent results (X2 = 1.24 and linewidthsup to 0.25 mmls). In addition, a second refining cycle was doneusing quadrupole splitting distributions (QSD), following theapproach of Gnnter et al. (2003), Rancourt (1994a, 1994b),and Rancourt and Ping (1991). Several fitting models with nn-constrained parameters-isomer shift (00), coupling parameter(01), center of a Gaussian component (~o), Gaussian width (o,,),and absorption area (A)-were tried to get a best fit. A modelbased on two sites (1 Fe2+ + 1 Fe3+) with two components forFe2+ and a single component for Fe3+ was finally chosen (X2 =

1.10) because increasing the number of Gaussian componentsdid not change the resulting distribution significantly. Results ofboth the Lorentzian and the QSD approach were in agreementand this gave us good confidence in the physical correctness ofthe distribution analysis. Uncertainties were calculated using thecovariance matrix and errors were estimated to be approximately±3% for both Fe2+ and Fe3+ absorption areas (Table 2).

X-ray powder diffraction

Powder diffraction data were collected on a fully automatedparallel-beam Bruker AXS D8Focus diffractometer, operating intransmission mode, equipped with a Peltier-cooled Si(Li) solidstate detector. Fibers were gronnd nnder ethanol in an agatemortar and subsequently placed in a 0.7 mm diameter borosilicateglass capillary. A compaction of ca. 70% (estimated from X -ray

a

1351

effective absorption measurements) was obtained via an ultra-sonic cleaner. An effective absorption measurement was carriedout by collecting the transmitted beam through the samples ItCE)and the incident primary beam Io(E), both in direct transmission.A preliminary scan indicated the presence of very minor dolomite(included in the Rietveld refinement), traces of iron oxides andcalcite (almost undetectable), and serpentine (two main reflec-tions at 12.5 and 25 °28 removed from the refinement). Rietveldrefinement used the GSAS crystallographic suite of programs(Larson and Von Dreele 1985) using the EXPGUI graphical userinterface (Toby 2001). The backgronnd was fit with a 36-termChebyshev polynomial of the first kind to model the amorphouscontribution arising from the capillary. Peak -shape was fit by theTCH pseudo-Voigt fnnction (Thompson et al. 1987) modifiedfor asymmetry (Finger et al. 1994). Refined variables were GY,and GW (tan 8-dependent and angle-independent, respectively)Gaussian parameters, LX and LY (1/cos 8- and tan 8-dependent)Lorentzian parameters, and S/L and H/L asymmetry parameters(constrained to be equal in magnitude). Starting structuralparameters of fibrous tremolite were those of Yang and Evans(1996), whereas those of Ross and Reeder (1992) were selectedfor dolomite. Isotropic displacement parameters were kept fixedthroughout the refinement to the values of reference data. Cellparameters, fractional coordinates for all non-hydrogen atoms,and site scattering for M 1, M2, M3, M4, and M4' were refined forthe fibers. Only cell parameters and scale factor were refined fordolomite. Following the same procedure reported in Gianfagnaet al. (2007), the geometry of the system was partly constrainednnder the following conditions: TlV-O X 8 = 1.625(25) A, 0-0X 12 = 2.655(40) A, MFI_O = 2.08(1) A, M2VI_0 = 2.08(5) A,M3VI-0 = 2.07(1) A, M4VIll_0= 2.51 (15) A, M4'VIll_0= 2.55(35)A. The weight associated with those observations was progres-sively reduced to two at the last stages of the refinement. How-ever, after a few cycles of refinement, the y fractional coordinatesofM4' moved toward M4 with a corresponding reduction of theoccupancy to zero, providing a clear indication of the presenceof a nonsplit M4 site. In keeping with the small cationic excessat M4 obtained from EMP analyses (0.01 apfu), the possible

b

FIGURE 1. SEM images of the Susa Valley tremolite: (a) tremolite vein containing minor calcite and iron oxides; (b) tremolite fiber with athinner termination.

1352 BALLIRANO ET AL.: CRYSTAL CHEMISTRY OF FIBROUS TREMOLITE, SUSA VALLEY, ITALY

TABLE 2. 57FeMbssbauer hyperfine parameters at room temperature for the fibrous tremolite from Susa ValleyLineshape X' Fe2+ Fe3+ Fe~:w(% Fetot) Fe~~rr (% Fetot)

1\.0 (mm/s) GA(mm/s) 00 (mm/s) Area (%) 1\.0 (mm/s) GA(mm/s) 00 (mm/s) Area (%)Lorentzian 1.24 1.88 1.14 33 0.80 0.20 19 19 16

2.90 1.13 48

QSD 1.10 1.90 0.18 1.14 35 0.86 0.40 0.12 20 20 172.88 0.17 45

Notes: Isomershift (00) with respect to a-iron. ForQuadrupole Splitting Distribution (QSD):y=0.194 rnrn/s,0, = 0 for both Fe" and Fe"; h.zh. = 1.Symbols accordingto Rancourt and Ping (1991).Fe;:wisjust the area of absorption peaks assigned to Fe", while Fe;:" isobtained from Fe;:wby applying the correction factor C= 1.22(Dyaret al. 1993). Estimated uncertainties are about 0.02 mm/s for hyperfine parameters, and no less than 3% for absorption areas.

occurrence of a partly occupied A site was also investigated.However, attempts to detect electron density at A, Am, and A2were unsuccessful.

Attempts to model the presence of preferred orientation bymeans of the generalized spherical harmonics description of VonDreele (1997) produced a small improvement of the fit as a resultof a J texture index of 1.122. Convergence was reached at R; =

5.64%, Rwp = 7.35%, R; = 3.35%, reduced X2 = 1.96, contribu-tion of the restraints to X2= 83.2. Experimental details and otherdata of the refinement are reported in Table 3, cell parametersand site scattering (s.s.) values in Table 4, fractional coordinatesand isotropic displacement parameters in Table 5, selected bonddistances in Table 6, and experimental, calculated, and differenceplots are displayed in Figure 2.

Fourier transform infrared spectroscopy

FTIR data were collected on a Perkin Elmer Spectrum Oneover the range 4000-400 cm': 64 scans at a nominal resolutionof 4 cm' were averaged. The instrument was equipped with aKBr beamsplitter and a TGS detector. The powdered sample wasmixed in a 2: 100 ratio with 200 mg ofKBr to obtain a transparentpellet. Measurement was done at room temperature.

RESUL TS AND DISCUSSION

Crystal chemistry

Inspection of the various EPM analyses suggests that thefibers present chemical homogeneity. This is confirmed by theabsence of relevant peak-broadening and/or asymmetry of theX-ray powder diffraction pattern. The lowest alkali content isrelated to the largest Ca content. FeOtat content spans a rangefrom 0.65 to 1.41 wt%, but no correlation between Ca and Fecontent was observed. This fact seems to indicate the absenceof a Ca f--7 M4Fe2+substitution scheme.

The Mossbauer spectrum offibrous tremolite from Susa Val-ley is typical of a paramagnetic material with some accessorymagnetic phases, the latter accounting for about 29% of total Fe(Fig. 3). The magnetic phases were identified as hematite (IS= 0.39 mm/s, H = 51 T, 19% of Fetat) and magnetite (IS = 0.30and 0.77 mm/s, H = 51 and 46 T, respectively, 10% of Fetat) andtheir contribution to the absorption spectrum was subtracted fromthe %Fe3+ of the amphibole. The spectrum of fibrous tremoliteis well-represented by three quadrupole doublets: the first twoshow IS values of about 1.1 mmls and QS values of about 1.9and 2.9 mm/s, and were assigned to Fe2+;the third shows an ISof about 0.2 mm/s and a QS of about 0.8 mm/s, and was assignedto Fe3+ (Table 2). A very close match was observed between the

TABLE 3. Experimental details of the X-ray powder diffraction datacollection and miscellaneous data of the refinement

InstrumentX-raytube

BrukerAXSD8 FocusCuat 40 kVand 40 mA(CuKa,= 1.540598 A)MultilayerX-raymirrorsRotating capillary (30 rpm)2 (2.30 divergence)lmm

Incident beam opticSample mountSoller slitsDivergence andantidivergence slitsDetector slit 0.2 mm (0.10

)

Detector Peltier-cooled solid state Si(Li)SolX28 range (") 5-155 (7501 data points)Step size (") 0.02Counting time (s) 30Rp (%),Rwp (%),RF (%) 5.64,7.35,3.35Reduced X' 1.964Restraints contribution to X' 83.2Refined parameters 97Peak cut-off (%) 0.02J 1.122GV,GW 45(2),21.7(6)LX,LY 0.6(1),3.0(3)S/L = H/L 0.0238(2)Amphibole wt% 99.644(3)Dolomite wt% 0.36(3)Note: Statistical descriptors as defined by Young (1993).

Fibers His! 1

Lambda 1.5406 A, LoS cycle 3041 Obsd. and DilI. Proliles

I. II IIII III 1111 111111111111 """111'"111111 1111111111111"'"'1.11""""'"11""'"'" '"111'""1111111111111"1111111111111_.,1 .,. , 1__ •• ,.,1

~~U -"---_---l __ ---'--__ -'--- ---'- "---_~

tUl 20.() 40.0 se.o 140.0IO().() 12(LOOCtO

2-Thcta, dcg

FIGURE 2. Experimental (dots), calculated (solid line), and differenceplots of the Rietveld refinement of the fibrous tremolite from SusaValley. Vertical markers refer, from above to below, to calculated Braggreflections of dolomite and tremolite. Two peaks of serpentine at 12.5and 25 °28 were removed from calculation.

results of Lorentzian and QSD analysis. Fe3+ proportions arequantified at 19% Fetat from direct area measurement (Fe;:w)and 16% when adjusting for the recoil-free fraction (Fe;~H)' assuggested by Dyar et al. (1993).

In the case of the tremolite-actinolite series, Burns and

BALLIRANO ET AL.: CRYSTAL CHEMISTRY OF FIBROUS TREMOLITE, SUSA VALLEY, ITALY

TABLE4. Unit-cell parameters and site scattering values (in electronsper formula unit) for the fibrous tremolite from Susa Valleyobtained from the structure refinement

Refinement Possiblesite partition Chemical dataQ (A) 9.84174(8)b (A) 18.05932(19) -c (A) 5.27876(6)~ (") 104.732(1)V (A3) 907.37(1)M4 40.20(12) Ca,9s;Naoos;KoOl (39.68)Sum Bsites 40.20 39.68Ml 24.98(14) AloOl;Fe~'os;Mg'9,;Mn002 (24.97)M2 24.50(14) Fe~'04;Fe6'o,;Mg'94 (24.84)M3 12.19(10) Fe~'o,;Mgo98 (12.28)Sum C sites 61.67 62.09

Note: Possiblesite partition isthe result of combining chemical, Miissbauer, andRietveld refinement data.

TABLE5. Fractional coordinates and isotropic displacement parame-ters (not refined) for the fibrous tremolite from Susa Valley

Site x y z U;,c(A')01 0.1139(4) 0.08679(24) 0.2178(10) 0.00802 0.1166(5) 0.17198(25) 0.7236(10) 0.00803 0.1085(5) 0 0.7137(12) 0.00804 0.3657(5) 0.24749(23) 0.7897(12) 0.00805 0.3454(5) 0.13364(23) 0.0985(11) 0.00806 0.3438(5) 0.11794(21) 0.5950(11) 0.00807 0.3387(6) 0 0.2893(15) 0.008Tl 0.28106(22) 0.08436(12) 0.2977(5) 0.005T2 0.28751(25) 0.17064(11) 0.8041(6) 0.005Ml 0 0.08738(18) 0.5 0.007M2 0 0.17656(20) 0 0.007M3 0 0 0 0.007M4 0 0.27737(12) 0.5 0.007H 0.206* 0 0.771* 0.030

* Fractional coordinates, taken from Yang and Evans(1996),unrefined.

Greaves (1971) attributed the Fe2+doublets with QS of 1.7-1.9and 2.8-2.9 mmls to the presence ofM2Fe2+and MIFe2+,respec-tively. More recently, many authors agreed to assign the dou-blet with lowest QS to M2Fe2+,but different assignments wereproposed for the doublets with highest QS, often suggesting anirresolvable combination of MI+M3Fe2+(see Gunter et al. 2003and references therein).

In the present work, according to the area of the Mossbauerabsorption peaks, Fe2+was preliminarily allocated at M2 (QS of1.88 mm/s, 40% of the total Fe2+)and at Ml + M3 (QS of2.90mm/s, 60% of the total Fe2+). Moreover, the Fe3+was assignedto represent occupancy at the M2 site, as consistently reportedby various authors for sodic amphiboles (Ernst and Wai 1970),strontian potassirichterite (Sokolova et al. 2000), ferrian winchite(Sokolova et al. 2001), winchite-richterite (Gunter et al. 2003),and fluoro-edenite (Gianfagna et al. 2007). Combining chemi-cal data and Mossbauer Fe3+/LFe ratios we obtain the followingaverage composition: Si02 58.51 %, Ti02 0.02%, AIP3 0.05%,Fe203 0.20%, MgO 23.74%, CaO 13.29%, MnO 0.13%, FeO0.99%, Na20 0.20%, K20 0.04%, F 0.07%, Cl 0.03%, H202.15% (estimated content to obtain a total of2 OH + F + Cl apfu),and the corresponding chemical formula: (Ca19SKoOlNaoOSh201(VIAloOIFet02Fe5+IIM~84Mno02booSi800022(OHI96Fo.03CloOlboo.Therefore, the sample represents a nearly ideal tremolite (CalLM = 0.389; M = Mg + Fe2++ Mn + Ni + Ti + vlFe3++ VICr3++VIAl), and Mg = 0.98 [Mg = Mg/(Mg + Fe2+)].

The measured cell volume of907.37(1) Ncompares favor-ably with values of906.5 N (Gottschalk et al. 1999),906.6 A3(Verkouteren and Wylie 2000), and 907.0 A3 (Yang and Evans

1353

100.0

99.5

~Q) 99.02''"EEi!' 98.Si"f-

98.0

Fibrous tremolite

+ expo spectrum-calc. spectrum- Fe2

+ (tremolite)- Fe3

+ (tremolite)- - - Fe3

'" (magnetite)- - - Fe2

.S

+ (magnetite)- - - Fe" (hematite)

97S +-~,-r--r~--,-~---,-~-.--~,--r--r~--,-~---,---r---o-10 -8 -6 -4 -2

Velocity (mm/s)

10

FIGURE 3. Room-temperature 57FeMossbauer spectrum of fibroustremolite sample from Susa Valley. Magnetic iron oxides were revealed

and subtracted from the Fe3+/Fetot ratio calculation.

1996) reported for pure tremolite (Ca/Mg = 2/5). Moreover, ittakes into account the presence of2.2% ferroactinolite content[Xp,A =(Fe2++ Mn)/(Fe2++ Mn + Mg)]. In particular, the chemicalcomposition and cell parameters of the fibers are close to samples9 and 31 ofVerkouteren and Wylie (2000).

Rietveld refinement indicates very marginal differences inbond distances relative to the reference data of Yang and Evans(1996). The mean Tl-O distance is slightly smaller than T2-0reported for C2/m amphiboles with no tetrahedrally coordinatedAl (Hawthorne 1981). Polyhedral distortion ~ shows comparablevalues for both T 1- and T2-centered tetrahedra. Site scattering ofMl , M2, and M3 sites consistently indicates the minor presenceof a scatterer heavier than Mg in agreement with both chemicaldata and the assignment of Mossbauer spectroscopy. A possiblesite assignment is proposed in Table 4. A remarkably good agree-ment is observed between site scattering derived from Rietveldrefinement and those from chemical data, largest differencesbeing smaller than 1.5%. This is fully consistent with the find-ings of previous works on fibrous amphiboles (Gianfagna et al.2003, 2007). Site partitioning, beside the constraints indicatedby Mossbauer spectroscopy, allocates 70% of the M1+M3Fe2+atMl and 30% at M3, to fulfill the requirement of only a slightlyincreased s.s. at M3 with respect to that of a Mg atom. Therefore,considering site multiplicity, nearly equal distribution of Fe2+may be observed over each one of the sites Ml , M2, and M3(Table 4), with a small preference for Ml , consistent with thefindings of Evans and Yang (1998) for the tremolite - actinolite- ferro-actinolite series.

The presence ofM1+M3Fe2+isconfirmed by FTIR spectroscopy(Fig. 4). In fact, besides the typical tremolite absorption bandat 3673-3675 cm' assigned to the vibration of the O-H dipolebonded to three VIMgcations, a well-developed band is observedat 3660 cm'. This latter was attributed to the MI+M3Fe2+environ-ment, according to results of Skogby and Rossman (1991).Moreover, no MI+M3Fe+3is present because absorption bands at~ = -50 cm' from the tremolite reference band (Raudsepp etal. 1987) are absent. No A cation is observed either, as wouldbe indicated by absorption bands at ~ = +55-60 cm' (Robertet al. 1989).

1354 BALLIRANO ET AL.: CRYSTAL CHEMISTRY OF FIBROUS TREMOLITE, SUSA VALLEY, ITALY

TABLE 6. Selected bond distances (A) and polyhedral distortion (Li x104) for the fibrous tremolite from Susa Valley

Presentwork YE96 Presentwork YE96TI-OlTI-05TI-06TI-07<TI-O>Li

1.592(4) 1.600(1) T2-02 1.627(4)1.624(5) 1.633(1) T2-04 1.598(4)1.649(5) 1.630(2) T2-05 1.654(6)1.630(2) 1.619(1) T2-06 "'1.C"65:;-::6"'(5:L)_---:-'-'::':::-?-'-'-1.624 1.620 <T2-0> 1.6341.6 0.6 Ll 2.1

1.612(1)1.587(1)1.656(2)1.676(1)1.6334.6

MI-Ol x2MI-02 x2MI-03x2<MI-O>Ll

2.080(5) 2.067(1) M2-01 x2 2.133(5) 2.134(1)2.087(5) 2.081(1) M2-02 x2 2.074(5) 2.088(1)2.071(4) 2.087(1) M2-04x2 2.028(5) 2.019(1)2.079 2.078 <M2-0> 2.078 2.0800.1 0.2 Ll 4.3 5.2

M3-01 x4M3-03 x2<M3-0>Ll

2.093(4)2.060(6)

2.073(1)2.062(2)

M4-02 x 2 2.375(5) 2.405(1)M4-04 x 2 2.306(5) 2.327(1)M4-05 x 2 2.784(5) 2.766(2)M4-06 x 2 2.565(4) 2.535(2)<M4-0> 2.508 2.508Ll 55 44

2.0820.6

2.0690.1

Note: Polyhedral distortion Ll as defined by Brown and Shannon (1973):

1 (R_R)2 _Ll = -;;L 'R where n is the number of ligands, R is the average bond

length and R, an individual bond length. Referencedata of Yangand Evans(1996)(YE96)from single-crystal analysis are reported for comparison purposes.

No correlations between mean bond distances <MI-O>,<M2-0>, and <M3-0> have been attempted because their dif-ferences are within the standard deviation of individual bonddistances, which gave uncertainties on the mean cationic radius<r«> ofo.oosA (see also Fig. 1 in Evans and Yang 1998). How-ever, the combined increase of both <M3-0> and ~ with respectto ideal tremolite (Yang and Evans 1996) is consistent with thepresence ofM3Fe2+.

Environmental and toxicological relevance

The problem of human exposure to airborne mineral dusts indaily life has recently become more and more relevant. Amongthose related to amphibole fibers, the examples of Libby (Mon-tana, U.S.A.) and Biancavilla (Sicily, Italy) are well documented(Gunter et al. 2007 and references therein). The case of SusaValley (Italy) is, in some aspects, even more peculiar becausein addition to the epidemiological investigation related to envi-roumental exposure to fibers, there is a need for a prediction ofexcavation effects focusing, in particular, on the amount offiberreleased into the environment.

The harmful potential of Susa Valley tremolite on humanhealth was recently shown to be very high. With respect to otherfibrous tremolites of the Western Alps, it shows a small reductionoffibrousness and a consistent increase of the surface area undergrinding. Moreover, from the toxicological point of view, suchtremolite has been proved to be very effective in the generationof reactive oxygen species (ROS) and in the activation of bio-logical reactivity (Turci et al. 2007). Mineral-induced ROS hasbeen observed to determine a strong release of'Ol-l free radicals,whose generation may be explained via an iron-catalyzed Haber-Weiss cycle (Fubini and Otero Arean 1999):

Reductant + Fe3+ ---> oxidized reductant + Fe2+;Fe2+ + O2 ---> Fe3++ 0;-;Or + 2H+ + e ---> H202;

Fe2+ + H202 ---> Fe3++ OH- + ·OH.

1.4 3673

1.2

3660

1.0IIIc~ 0.8~.c«

0.6

0.4

0.2

3740 3720 3700 3680 3660 3640 3620 3600

Wavenumber (ern")

FIGURE 4. FT-IR spectrum in the 3750-3600 cm' wavenumberrange.

The role of free radicals in inducing DNA damage andsubsequent carcinogenesis is well recognized in scientific lit-erature. However, in the case of tremolite this is not the onlymechanism because iron content is generally small as comparedto, for example, Libby winchite (Meeker et al. 2003; Gunter etal. 2003) and Biancavilla fluoro-edenite (Gianfagna et al. 2007).Cytotoxicity of Susa Valley tremolite onAS49 lung cells has beenshown to be comparable to cytotoxicity of crocidolite: this is dueto its oxidative stress, measured from release ofLDH enzyme,as well as to its inhibition of anti -oxidative defenses, measuredfrom the reduction of the pentose phosphate pathway (Gazzanoet al. 2007). According to these very challenging findings, thecytotoxic/oncogenic pathway following the tremolite/cell inter-action seems to be dependent on different fiber morpho-structuraland crystal-chemical features as well as on surface chemistry.Therefore, a full characterization (morphology, resistance tocomminution, crystal structure, crystal chemistry, Fe3+/Fetot

ratio, cation site partitioning) of different fibrous amphibolescoupled with both in vitro and in vivo analyses (to determinetheir cytotoxicity) would be useful.

ACKNOWLEDGMENTSThis research was carried out within CNR-IGAG and CNR-IGG research

priorities and under the financial support of Universita di Roma "La Sapienza."Thanks are due to Elena Spaziani for help in FTIR data acquisition.

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