Asbestos fibre identification vs. evaluation of asbestos hazard in ophiolitic rock mélanges, a case...

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Environmental Earth Sciences ISSN 1866-6280Volume 72Number 9 Environ Earth Sci (2014) 72:3679-3698DOI 10.1007/s12665-014-3303-9

Asbestos fibre identification vs. evaluationof asbestos hazard in ophiolitic rockmélanges, a case study from the LigurianAlps (Italy)

Gianluca Vignaroli, Paolo Ballirano,Girolamo Belardi & Federico Rossetti

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ORIGINAL ARTICLE

Asbestos fibre identification vs. evaluation of asbestos hazardin ophiolitic rock melanges, a case study from the Ligurian Alps(Italy)

Gianluca Vignaroli • Paolo Ballirano •

Girolamo Belardi • Federico Rossetti

Received: 17 September 2013 / Accepted: 18 April 2014 / Published online: 11 May 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract In recent years, the high incidence of harmful

health effects through inhalation of airborne asbestos from

amphibole-bearing rock melanges has been thoroughly

documented. Here, we present a field-based, multi-scale

geological approach aimed at illustrating the occurrence of

amphibole fibrous mineralisation in an ophiolitic suite from

the Ligurian Alps (Italy) and discussing the implication on

in situ determination of the asbestos hazard. The rock

melange is composed of plurimetre-sized blocks of dif-

ferent lithotypes (metagabbro, serpentinite, chloritoschist)

juxtaposed by the meaning of tectonic structures. The

geological-structural survey revealed that the fibrous min-

eralisation is localised in specific structural sites of the rock

volume, including veins and schistosity. Both micro-

chemical and crystal structure analyses on selected fibrous

samples revealed that actinolite fibres grow in veins within

the metagabbro and in chloritoschists, while fibrous trem-

olite occurs in serpentinite schistosity. The morphological

features of these amphibole fibres have been analysed in

TEM images and used for classifying them as ‘‘asbesti-

form’’ or ‘‘non-asbestiform’’. The results show that the

asbestos hazard determination is not unequivocally identi-

fied when different procedures for asbestos fibre identifi-

cation and classification are applied. This may have impact

on normatives and regulations in defining environmental

hazards due to asbestos occurrence.

Keywords Amphibole � Asbestos hazard � Ophiolite

melange � Rock petrography � Mineralogy � Ligurian Alps

Introduction

Five fibrous amphiboles (anthophyllite, tremolite, actinolite,

crocidolite, and amosite) and the serpentine chrysotile are

the six minerals currently regulated by the normative as

‘‘asbestos’’ (e.g. Ross et al. 1984; World Health Organiza-

tion—WHO, 1986; NIOSH 2011). Their occurrence in both

built and natural environments determines the main issue for

evaluating the asbestos hazard (Lee et al. 2008; Gunter

2010). Actually, the combination of mineralogical (e.g.

Gunter et al. 2007; Gunter 2010), epidemiological (e.g. Doll

1955; Lippmann 1990; Rey et al. 1994; Honda et al. 2002;

Cattaneo et al. 2006) and environmental (e.g. Rohl et al.

1977; Wagner 1991; Pan et al. 2005) studies asserts that

serious health risks are directly connected with persistent

inhalation of asbestos particles. In particular, amphibole

asbestos are listed as a Group I human carcinogen material by

the international world health authorities (IARC (Interna-

tional Agency for Research on Cancer) 1987, 2012; Health

and Safety Executive 1997; WHO 1986; Kazan-Allen 2005).

The insights coming from the amphibole asbestos studies are

being extended also to other fibrous minerals not included in

the asbestos group (e.g. Groppo et al. 2005; Sullivan 2007).

G. Vignaroli (&) � F. Rossetti

Dipartimento di Scienze, Sezione di Geologia, Universita Roma

Tre, Largo S.L. Murialdo, 1, 00146 Rome, Italy

e-mail: [email protected]

P. Ballirano

Dipartimento di Scienze della Terra, Sapienza Universita di

Roma, P.le A. Moro, 5, 00185 Rome, Italy

P. Ballirano

Laboratorio Rettorale Fibre e Particolato Inorganico, Sapienza

Universita di Roma, P.le A. Moro, 5, 00185 Rome, Italy

G. Belardi

Istituto di Geologia Ambientale e Geoingegneria, CNR, Area

della Ricerca di Roma 1, Via Salaria Km 29,300, Monterotondo

Stazione, 00015 Rome, Italy

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Environ Earth Sci (2014) 72:3679–3698

DOI 10.1007/s12665-014-3303-9

Author's personal copy

The asbestos hazard in natural environment occurs

whenever disturbing processes produce airborne fibres,

which may be individual fibrils or fibrillar bundles. Due to

their small size and low density, the asbestos fibres can be

easily transported and dispersed into the atmosphere or

water supplies which become contaminated (Fig. 1). Ero-

sion and mobilisation by wind and water constitute natural

processes for fibre dispersion. Similarly, the processing of

the bulk materials in ore mining and production (crushing,

grinding, and milling) can be a significant source of par-

ticulates, if uncontrolled, and may induce environmental

hazard. Although commercial deposits of asbestos are

restricted to a few countries (Canada, Asia, Latin America,

and Eastern Europe), non-economic deposits of asbestos

fibres occur in several mafic and ultramafic rock formations

(e.g. the ophiolite sequences) cropping out in many oro-

genic belts worldwide. Accordingly, the rock management

for industrial, engineering, and others uses (e.g. Marinos

et al. 2006; Pereira et al. 2007) is subjected to predictive

assessment of the asbestos content for mitigating and

reducing the potential environmental hazard (e.g. Rohl

et al. 1977; Labagnara et al. 2012; Liebenberg et al. 2012;

Lescano et al. 2013).

The evaluation of the asbestos hazard is based on a

counting method of the particles with fibrous morphology

dispersed in the transporting medium. By definition, the

fibrous morphology of a particle is determined by an aspect

ratio (A.R.: length divided by width) exceeding 3:1. Any-

way, there is increasing consensus in considering that the

use of a minimal 3:1 aspect ratio is questionable for clas-

sifying a particle as asbestiform (Wylie et al. 1985;

AHERA (Asbestos Hazardous Emergency Response Act)

1987; Harper et al. 2008; Van Orden et al. 2008; NIOSH

2011). Higher aspect ratios (5:1, 10:1, 20:1) have been

proposed to distinguish real asbestiform amphiboles from

fibres originated by preferential splitting of amphibole

crystal along planes of structural weakness (amphibole

cleavage particles). The so-called ‘‘asbestos structures’’ (or

‘‘true asbestos structures’’) consist of fibres, bundles,

fibrous components of clusters, or matrices as defined, for

example, in ISO 13794 or AHERA (1987). The ‘‘asbesti-

form’’ term refers to particles that exhibit (most of) the

properties commonly associated with asbestos (i.e. high

tensile strength, flexibility, and resistance to chemical

attack). Typically, shape and dimension of an asbestiform

fibre formed during crystallisation process differ from

those of fibre fragments due to mechanical cleavage.

Because cleavage fragments are elongated structures

formed by the fragmentation of the massive or acicular

particles, they are excluded from the ‘‘asbestiform’’

definition.

Although the dimensional criteria for counting and the

importance of using instruments with the appropriate res-

olution have been critically reviewed by Dodson et al.

(2003), different procedures complementing or overcoming

the A.R. criterion have been proposed for refining the

classification of amphibole particles into asbestos or non-

asbestos. Berman and Crump (2003) proposed in their

asbestos risk model to take into consideration the structures

longer than 10 lm and thinner than 0.4 lm (A.R. [25:1)

using the counting and characterisation rules defined in

ISO 10312. A more recent method is based on microscopic

measurements and considers that all particles should be

counted on the basis of the width criterion of 1 lm (Harper

et al. 2008). This limit has been fixed from the conven-

tional definition of respirable particle. The procedure pro-

posed by Chatfield (2008) is based on the combination of

the width and the aspect ratio of particles and, in this case,

the amphiboles are classified as asbestos if thinner than

1.5 lm and simultaneously characterised by an A.R.

exceeding 20:1. A further method is based on a complex

multi-analytical procedure that takes into consideration the

chemical and morphological features of the individual

amphibole fibre (Van Orden et al. 2008, 2009). The

selection of the counting method has extreme implications

in assessing the asbestos hazard inasmuch no evidence of

demonstrable cancer effects from exposure to amphibole

cleavage has been found so far (Williams et al. 2013), and

the toxicity of short fibres is still the matter of debate

(Dodson et al. 2003).

In natural environment, the evaluation of the asbestos

hazard commonly relies on measuring the concentration of

dispersed fibres in air (e.g. Lange et al. 1996; Zakrzewska

et al. 2008) and soils/water (e.g. Burilkov and Michailova

1970; Hardy et al. 1992; Emmanouil et al. 2009). On the

contrary, very little effort has been paid to develop proto-

cols aimed at the quantification of the asbestos concentra-

tion in rocks. In addition, few works have been devoted to

elaborate an approach for the in situ quantification of free

asbestos fibres (Bellopede et al. 2009; Giacomini et al.

2010; Lescano et al. 2013). The difficulty for assessing the

in situ occurrence of asbestos depends on the detailed

Fig. 1 Flowchart illustrating the asbestos fibres pathways in the

environment (modified and redrawn after Schreier 1989)

3680 Environ Earth Sci (2014) 72:3679–3698

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knowledge of the geological properties of the asbestos-

bearing rocks, which include the lithology (e.g. Ross and

Nolan 2003; Van Gosen 2007; Hendrickx 2009) and the

tectonic–metamorphic conditions that favoured fibrous

mineralisation within the rock volume (e.g. Evans 1977;

Hoogerduijn Strating and Vissers 1994; Karkanas 1995;

Ross and Nolan 2003; Andreani et al. 2005; Compagnoni

and Groppo 2006; Vignaroli et al. 2011).

This paper is aimed at discussing the in situ asbestos

hazard by illustrating the identification and classification of

amphibole fibrous mineralisation occurring in an ophiolitic

rock suite (metagabbro-bearing melange) from the Liguri-

an Alps (Italy). A geological, field-based approach is used

for describing the presence of geological heterogeneities

(lithotypes, deformation structures, and secondary miner-

alisations), while multi-analytical laboratory techniques,

including petrographic microscopy, X-ray powder diffrac-

tion (XRPD), and transmission electron microscopy (TEM)

investigations, have been integrated for discriminating the

asbestos structure of collected amphibole fibres. The results

Fig. 2 a Geological-structural map of the study area (indicated by the

white square) and surroundings (redrawn and modified after Capponi

et al. 2006); b simplified block diagram illustrating the main

lithologies cropping out in the study area and the occurrence of the

main deformation structures; c panoramic view on the tectonic

contacts between different lithologies (metagabbro, chloritoschists,

serpentinites) marked by the occurrence of brittle fault systems;

d panoramic view on the fault systems that cross cut and dislocates a

set of metamorphic veins developed within the metagabbro volume

Environ Earth Sci (2014) 72:3679–3698 3681

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are used for (1) comparing the different classification

methods for the asbestos fibre identification, (2) qualita-

tively evaluating the asbestos hazard in rock complexes,

and (3) discussing the issue of amphibole asbestos identi-

fication and classification in a natural site.

The field-based, multi-scale approach

This work is based on a multidisciplinary and multi-scale

approach that integrates the contributions deriving both

from field survey and laboratory. The field geological

survey is aimed at defining the geological complexities

within the rock volume at the mesoscale, with particular

emphasis on the lithotype, rock deformation fabrics, and

occurrence of secondary mineralisation. The necessity to

discriminate the geological-structural conditions of a rock

volume is imperative when considering rock melanges,

which are intrinsically characterised by different lithotypes

showing discontinuous shapes, sizes and deformation fab-

rics. This is a priority, since asbestos mineralisation does

not appear homogeneously dispersed within the rock vol-

ume; instead it is restricted to peculiar geological settings/

environments that should be treated carefully. The geo-

logical survey was then firstly focused on collection of

samples representative of the range of lithotypes, defor-

mation structures, and mineralisations addressed to a series

of laboratory analyses (see the Appendix for experimental

conditions). Microscale observations were addressed (1) to

define the mode of fibre growth (e.g. as individual or in

bundles), and (2) to constrain the relationships between

fibres nucleation and surrounding matrix. The first point

has implication on the determination of the amount of

fibres occurring in rock mass; the second has inference on

the potential of the rock to release free fibres. In this work,

the types of fibrous minerals were characterised in terms of

their geometrical relationships, occurrence and distribution

in relation to the primary and secondary structures of the

rock volume, by combining optical transmitted light

microscopy and scanning electron microscopy (SEM) on

polished thin sections. The crystal chemical and structural

characterisation was finalised to the identification of the

fibrous minerals, according to the asbestos nomenclature as

provided by the normative. Mineral chemistry of single

sampled fibre was obtained by combining electron micro-

probe analyses (EMPA) and structure refinements by the

Rietveld method on XRPD data. The morphological

parameters (i.e. length, width, shape, cleavage) of single

fibres have been extrapolated through image analysis of

particles resting on filters using a stepwise TEM exami-

nation. The results have been plotted in an aspect ratio/

width diagram according to different classification criteria

of fibres (Berman and Crump 2003; Harper et al. 2008;

Chatfield 2008). A further morphological characterisation

of the analysed fibres has been performed according to the

analytical procedure proposed by Van Orden et al. (2008).

Lithology and field structures

The investigated area is part of an ophiolitic suite,

belonging to the Ligurian Alps (north Italy; see insert in

Fig. 2a), composed of variably metamorphosed mafic and

ultramafic bodies and discontinuous cover successions. The

ophiolitic suite experienced a polyphasic tectono-meta-

morphic evolution with development of ductile and brittle

deformation structures (e.g. Hoogerduijn Strating 1994;

Capponi and Crispini 2002). Ductile structures are mainly

represented by S-tectonites (and subordinate SL-tectonites)

dominantly hosting sodic- and calcic-amphibole-bearing

mineral assemblages in mafic precursor rocks, whereas

brittle structures include fracture systems and fault damage

zones (e.g. Vignaroli et al. 2005, 2009; Federico et al.

2007, 2009; Crispini et al. 2009).

A kilometre-scale lens of metagabbro defines the main

lithotype in the study area (Fig. 2a). The metagabbro lens

has a N–S elongated shape. The internal portion of the

metagabbro is generally homogeneous, but locally contains

metre-scale boudins of chloritoschists and talcschists. The

metagabbro shows a dominant massive texture, locally

Table 1 List of selected

samples and mesoscale featuresLithotype Structural domain Fibrous amphibole Fibre length

TB15 Metagabbro Metamorphic foliation Not observed within

the foliation

TB10b Metamorphic vein in

Metagabbro

Within vein walls Isolated soft tufts Up 3

centimetres

LIV335 Metamorphic vein in

metagabbro

Roughly perpendicular to

the vein walls

Carpet Up to 1

centimetre

TB4a/

TB4a bis

Chloritoschist Metamorphic foliation Isolated, rigid

particles

Few

millimetres

TB Serpentinite Metamorphic foliation Soft tufts Up to 2

centimetres


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evolving in a steeply-dipping (50–70�) NW–SE striking

planar fabric. The body is cut across by a set of 2–3 cm-

thick metamorphic veins, showing variable spacing (from

20 to 30 centimetres up to several metres), and high per-

sistence ([10 m). Laterally, the metagabbro is in contact

with a huge sequence of antigorite serpentinites (see the

block diagram in Fig. 2b). The boundaries between

different lithotypes correspond to steeply-dipping bands of

highly strained fault rocks. Major faults have roughly

planar surface and are often characterised by decimetre-to-

metre thick damage zone and fault core (sensu Caine et al.

1996). Sporadic mineralisation, mainly consisting of iron

oxides and subordinately talc, decorates the fault surfaces.

Faults dismember the metagabbro body, and often produce

Fig. 3 Samples mesoscale features. a Pegmatoidal structure of the

metagabbro defined by magmatic pyroxene (Px) rimmed by coronas

of plagioclase (Pl) and tiny green amphibole (Am); b syn-greenschist

metamorphic foliation in metagabbro; c example of the metamorphic

vein developing within the metagabbro volume, with evidence of the

fibrous amphibole mineralisation (in the inserts); d well-foliated

chloritoschists with localisation of the selected sample (in the insert);

e foliated serpentinites and fibrous amphibole (in the insert)


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alternating metre thick repetition of metagabbro-chlor-

itoschists-serpentinites. The faults systematically truncate

and dissect the metamorphic vein sets (Fig. 2c, d). The

above-mentioned structures testify for a main brittle char-

acter of the metagabbro deformation during its exhumation

within the enveloping serpentinite matrix.

The major issues that can be extracted from the field

survey are: (1) the internal fabric of the metagabbro body is

characterised by a pervasive schistosity; (2) the metamor-

phic veins constitute a locus of secondary metamorphic

mineralisation, different to those of the internal metagab-

bro fabric; (3) variably sized and shaped lenses of chlori-

toschists and talcschists are embedded within the

metagabbro and thus define an abrupt change in lithology;

(4) deformational structures (mainly fault zones) control

contacts between the metagabbro, chloritoschists, talcs-

chists, and serpentinites. Taking into consideration those

aspects, the sampling strategy has been addressed to

investigate in detail these geo-diversities. The mesoscale

characteristics of the selected samples are summarised in

Table 1.

The massive metagabbro (sample TB15) shows a pri-

mary pegmatoid texture made of coarse-grained clinopy-

roxene–plagioclase assemblage, green to purple in colour

(Fig. 3a). The main metamorphic overprint consists of syn-

greenschist mineralogical assemblage (green amphibole,

plagioclase, chlorite, epidote) that rims the magmatic

clinopyroxene (Fig. 3a) and also produces a pervasive

foliation (Fig. 3b). Fibrous mineralisation does not appear

at the mesoscale within the metamorphic foliation of the

metagabbro. Metamorphic veins (samples TB10b and

LIV335) have sub-planar surface (Fig. 3c) and are filled by

albite plagioclase in blocky texture, seldom in association

with fibrous amphibole (inserts in Fig. 3c). These fibres are

Fig. 4 Samples microscale

features. a Rim of plagioclase

(Pl) and prismatic/tabular

amphibole (Am) around

magmatic pyroxene (Px) in

metagabbro; b and c plagioclase

blocky structure enclosing

fibrous amphibole in

metamorphic vein;

d metamorphic foliation in

chloritoschists with fibrous

amphibole and talc (Tlc)

rimming the chlorite (Chl)

porphyroblasts; e pervasive

foliation in serpentinites marked

by the alignement of fibrous

amphibole and antigorite (Atg)


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whitish to green in colour. They are arranged to form both

isolated soft bundles with fibres up 2 cm of length (sample

TB10b) and rigid carpets disposed roughly perpendicular to

the boundaries of the vein (sample LIV335). Lenses of

chloritoschistes (sample TB4a) show an internal fabric

composed by a well-developed foliation (Fig. 3d) defined

by the chlorite-talc ± amphibole mineralogical associa-

tion. Very thin amphiboles are also observed in micro-fold

domains preserved within the metamorphic foliation.

Serpentinites show both massive and foliated (sample TB)

mesoscale texture. In massive one, the primary lherzolithic

texture (with occurrence of pyroxene porphyroclasts)

dominates, while secondary antigorite and amphibole

crystallise in the millimetre-spaced pervasive foliation

(Fig. 3e). Soft, ductile agglomerate of fibrous whitish-to-

green amphibole (insert in Fig. 3e) occurs disposed along

the foliation.

Laboratory analyses

Sample petrography

At the thin section scale, the main textural feature in

metagabbro (sample TB15) is represented by rims of fine

matrix of plagioclase and amphibole around large pyroxene

crystals (Fig. 4a). Amphibole is also variably distributed

within the foliation defining prismatic-to-acicular crystals

with width exceeding 5 lm. Samples from metamorphic

veins (TB10b and LIV335; Fig. 4b, c) show a blocky

texture composed by large grains of plagioclase. Amphi-

bole occurs as fibrous agglomerates accommodated within

interstices between plagioclase. The fibres tend to distrib-

ute from the interstices to the plagioclase crystal rims,

often superimposing to them. Fibre terminations show

cleavage and formation of individual smaller fibres

(fibrils). In chloritoschists (sample TB4a), large chlorite

grains are surrounded by thin foliation where acicular-to-

fibrous amphibole is aligned along the foliation surface

(Fig. 4d). Amphibole crystals tend to coalesce rather than

to be individual. Amphibole crystals have length up to

50 lm. The most evident microstructural feature in ser-

pentinite (sample TB) is a sub-millimetre-spaced meta-

morphic foliation where fibres of antigorite and amphibole

are interdigitated (Fig. 4e). Amphibole has width not

exceeding 5 lm and length of 10–20 lm.

Amphibole crystal chemistry and structure

Average chemical compositions and min–max composi-

tional ranges from EMPA of the analysed amphiboles are

reported in Table 2 and the corresponding crystal chemical

formulae are listed in Table 3. Amphibole classification is

reported in Fig. 5, distinguishing between non-fibrous

Table 2 Average chemical composition of the analysed amphiboles

TB TB4a TB4a bis TB10b LIV335

SiO2 58.31 (57.28–59.38) 57.18 (56.77–57.55) 58.65 (58.29–58.87) 55.51 (55.37–55.67) 55.14 (54.57–55.96)

TiO2 0.01 (0.00–0.02) 0.05 (0.02–0.12) 0.04 (0.02–0.07) 0.04 (0.01–0.09) 0.03 (0.00–0.06)

Al2O3 0.07 (0.03–0.14) 0.46 (0.26–0.77) 0.12 (0.05–0.15) 1.66 (1.60–1.72) 1.83 (1.13–2.53)

Cr2O3 0.01 (0.00–0.05) 0.03 (0.00–0.06) 0.01 (0.00–0.03) 0.05 (0.03–0.07) 0.01 (0.00–0.04)

FeOtot 1.94 (1.67–2.40) 7.47 (7.05–7.79) 4.96 (4.82–5.04) 11.26 (10.73–11.78) 12.28 (10.81–13.71)

MnO 0.15 (0.12–0.19) 0.43 (0.31–0.50) 0.22 (0.18–0.28) 0.21 (0.18–0.24) 0.15 (0.08–0.23)

MgO 23.05 (22.75–23.45) 19.18 (18.90–19.58) 21.36 (21.11–21.67) 16.49 (15.89–17.32) 15.77 (14.92–16.98)

CaO 13.19 (13.01–13.46) 12.33 (12.27–12.48) 12.74 (12.63–12.80) 11.97 (11.77–12.08) 11.85 (11.34–12.14)

Na2O 0.14 (0.07–0.24) 0.25 (0.15–0.41) 0.16 (0.12–0.21) 0.49 (0.42–0.60) 0.53 (0.31–0.82)

K2O 0.04 (0.01–0.11) 0.05 (0.04–0.05) 0.03 (0.01–0.08) 0.06 (0.04–0.08) 0.04 (0.00–0.19)

F 0.06 (0.00–0.16) 0.03 (0.00–0.08) 0.05 (0.00–0.18) 0.00 (0.00–0.00) 0.07 (0.00–0.19)

Cl 0.00 (0.00–0.00) 0.02 (0.00–0.04) 0.02 (0.00–0.03) 0.03 (0.00–0.09) 0.01 (0.00–0.03)

H2Oa 2.15 2.12 2.16 2.10 2.06

total 99.12 99.60 100.52 99.87 99.76

-F,Cl -0.03 -0.02 -0.03 -0.01 -0.03

99.09 99.58 100.49 99.86 99.73

Fe2O3 1.16 0.72 – 0.92 1.48

FeO 0.96 6.76 – 10.46 10.98

Min–max compositional ranges are reported in italica Calculated assuming OH ? F ? Cl = 2 apfu


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amphiboles (from metagabbro texture) and fibrous amphi-

boles (from metamorphic veins, chloritoschists, and

serpentinites).

The analysed amphibolic fibres show a small to mod-

erate compositional variability the only exception being

sample TB4a. In fact, in this case two different composi-

tional populations have been observed. According to the

Mg/(Mg ? Fe2?) ratio, fibres are classified as tremolite

(TB and TB4a bis) and actinolite (TB4a, TB10b, and

LIV335), respectively. The iron content spans a range from

ca. 2 to ca. 12 % FeOtot. Sample TB4a mainly contains

actinolite fibres (Mg/(Mg ? Fe2?) = 0.835), tremolite

being largely subordinate (Mg/(Mg ? Fe2?) C 0.884).

Due to this quantitative ratio it is possible to identify

actinolite as the amphibole occurring in the well-developed

foliation in association with chlorite-talc. Accordingly,

tremolite is the very thin amphibole observed in micro-fold

domain of the metamorphic foliation. A Fe2?/Fe3?

partition of tremolite was not performed because of the

impossibility to extract structural information from the

Rietveld refinement of the diffraction pattern of the TB4a

sample. In fact, attempts to model the diffraction data using

two amphibole structures failed because of the massive

prevalence of actinolite over tremolite. Therefore, classi-

fication of such tremolite fibres was performed considering

all iron as divalent. This is justified by the fact the calcu-

lated Mg/(Mg ? Fe2?) ratio of 0.884 represents the lower

limit, as the occurrence of Fe3? would eventually increase

such value without altering the classification as tremolite.

A magnified view of the four diffraction patterns is

reported in Fig. 6. Accessories phases occur in relatively

small amounts: antigorite (TB), chlorite (TB and TB10b),

quartz (TB, TB10b, and LIV335), albite (TB10b), and

dolomite (TB10b). Exploiting the features of the solid-state

detector, a qualitative analysis of the iron content has been

possible (see inset of Fig. 6). In fact, from visual evaluation

Table 3 Crystal chemical

formulae of amphiboles

calculated on the basis of

O ? F ? Cl = 24 atoms per

formula unit before (left) and

after (right) Fe2?/Fe3? partition

a Calculated \ M–O [ on the

basis of C population using the

cation ionic radii taken from

Shannon (1976) and a VIO

radius of 1.36A. The latter value

has been selected to obtain the

best fit with the M–O distances

from structure refinementsb Calculated assuming that all

Fe = Fe2?. Therefore, this

value represents the lower limit,

as the occurrence of Fe3? would

eventually increase such value

without altering the

classification as tremolite

TB TB4a TB4a bis TB10b LIV335 TB TB4a TB10b LIV335

T

Si 8.022 8.019 8.048 7.899 7.891 7.999 8.005 7.882 7.862

Al 0.000 0.000 0.000 0.101 0.109 0.001 0.000 0.118 0.138

Sum 8.022 8.019 8.048 8.000 8.000 8.000 8.005 8.000 8.000

C (M1 ? M2 ? M3)VIAl 0.011 0.076 0.019 0.177 0.200 0.010 0.076 0.160 0.170

Fetot 0.223 0.876 0.569 1.340 1.470

Fe3? 0.120 0.079 0.098 0.159

Fe2? 0.110 0.797 1.242 1.311

Mg 4.728 4.011 4.370 3.499 3.365 4.715 4.004 3.491 3.353

Mn 0.006 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Ti 0.001 0.005 0.004 0.004 0.003 0.001 0.005 0.004 0.003

Cr 0.002 0.005 0.002 0.009 0.000 0.002 0.005 0.008 0.000

Sum 4.971 4.973 4.964 5.029 5.038 4.958 4.966 5.003 4.996

s.s. (e-) 62.9 72.1 67.6 78.1 79.8 62.6 72.0 77.7 79.2

C \ M–O [a 2.079 2.085 2.087 2.087

Fe2?/Fetot 0.478 0.912 0.927 0.892

B (M4)

Ca 1.944 1.853 1.873 1.825 1.817 1.939 1.850 1.821 1.810

Mn 0.012 0.051 0.026 0.025 0.018 0.017 0.051 0.025 0.018

Na 0.037 0.068 0.043 0.135 0.147 0.037 0.068 0.135 0.147

K 0.007 0.009 0.005 0.011 0.007 0.007 0.009 0.011 0.007

Sum 2.000 1.981 1.948 1.996 1.989 2.000 1.978 1.992 1.982

s.s. (e-) 39.7 39.3 38.7 38.8 38.6 39.7 39.2 38.8 38.4

O3

OH 1.973 1.983 1.977 1.993 1.967 1.968 1.980 1.989 1.969

F 0.026 0.013 0.022 0.000 0.032 0.026 0.013 0.000 0.032

Cl 0.000 0.005 0.005 0.007 0.002 0.000 0.005 0.007 0.002

Sum 1.999 2.001 2.004 2.000 2.001 1.994 1.998 1.996 2.003

Mg/(Mg ? Fe2?) 0.884b 0.977 0.834 0.738 0.719

Classification Tr Tr Ac Ac Ac


123


of the EDX spectra (acquisition time of 24 h), simulta-

neously collected with the corresponding diffraction pat-

tern, it is possible to observe proportionality between Fe

content (expressed as atoms per formula unit, apfu) and the

height of the Fe Ka and Fe Kb fluorescence peaks for

the four analysed samples. The apparent deviation from the

trend of sample TB, which shows a peak higher than

expected, is due to the contribution of ca. 16 wt% of

antigorite containing ca. 6 % of FeO as compared to ca.

1.9 % of tremolite. The Rietveld plots of sample TB4a is

reported as example in Fig. 7. Quantitative phase analyses

(QPA), microstructural parameters e0 and Lvol, fibres cell

parameters, and miscellaneous data of the four samples are

shown in Table 4, selected bond distances, site scattering

(s.s.), and polyhedral distortion D (Brown and Shannon,

1973) in Table 5.

The mean T1-O distance is consistently slightly smaller

(1.616–1.623 A) than T2-O (1.634–1.647 A) as reported

for C2/m amphiboles with no or little tetrahedrally-coor-

dinated Al (Hawthorne, 1981). Slightly larger \T2-

O[ bond distances positively correlate with the occurrence

of ca. 0.1 IVAl apfu consistently with the Al site-preference

T2 » T1 (Hawthorne, 1981). Polyhedral distortion D shows

larger values for T2-centred tetrahedra as compared to T1.

Refined \M–O[ bond distances are in agreement with

those of Evans and Yang (1998) for tremolite-actinolite

samples of similar chemical composition. The \M1,2,3-

O[ bond distance increases as the overall iron content

increases. Site scattering of M1, M2, and M3 sites indi-

cates, as expected, the presence of a scatterer heavier than

Mg in agreement with chemical data.

The criteria for performing an indirect Fe2?/Fe3? par-

tition were based on the calculation of the \ M1,2,3-

O [ bond distance from the site population arising from

the conventional assignment to the C group sites, following

Hawthorne (1981). The \ M1,2,3-O [ bond distances

were calculated using the cation ionic radii taken from

Shannon (1976) and a VIO radius of 1.36 A.

Several cycles of iterative adjustments of the Fe2?/Fe3?

ratio were performed until the best fit with the \ M1,2,3-

O [ distances from the corresponding structure refine-

ments was achieved. Accordingly, the three TB4a, TB10b,

and LIV335 actinolite samples are characterised by a

nearly constant 0.9 Fe2?/Fetot ratio. Differently, the TB

tremolite sample has a significantly smaller 0.48 Fe2?/Fetot

ratio. As a further result of the Fe2?/Fe3? partition, recal-

culated crystal chemical formulae show a reduction of the

Si content at the T sites, originally exceeding 8 apfu

(Table 3).

The same procedure was adopted to obtain the indi-

vidual M1, M2, and M3 site partition. In this case a double

check was applied involving both the mean cation radius,

calculated from site partition and from the refined bond

distance, and the site scattering, calculated as well from

site partition and from the refined bond distance (Table 6).

The average deviation of the calculated mean cation radius

from the refined value is of ca. 0.003 A.

The TB tremolite sample allocates all available Fe3? at

M2 and all Fe2? at M1. The actinolite samples have a more

complex iron distribution pattern. In detail, a Fe2?

M2 [ M1 [ M3 site-preference has been consistently

observed. As far as the Fe3? distribution is involved, ferric

iron is allocated at M1 in sample TB4a, at M1 = M3 in

sample TB10b, and at M1 = M2 in sample LIV335.

The site scattering of the C group sites derived from

Rietveld refinement and those from chemical data differs.

Fig. 5 Amphibole diagram classification (after Leake et al. 1997)

Fig. 6 Magnified view of the four diffraction patterns. As the only

detectable reflection of chlorite occurred at ca. 6� 2h, the 5–7� 2hangular range was removed from refinement of the diffraction pattern

of sample TB. Inset: Inset: EDX spectra, simultaneously collected for

the four analysed samples (acquisition time of 24 h). Relevant

reflections of accessory phases are labelled as follow: Ab albite; Ant

antigorite, Dol dolomite; Qtz quartz


123


In particular, the scattering from site partition, and there-

fore from EMPA, is higher than that from structure

refinement and such deviation increases as the s.s. increa-

ses. This fact is fully consistent with the findings of pre-

vious works on fibrous amphiboles (Pacella et al. 2008;

Ballirano et al. 2008; Andreozzi et al. 2009) as can be seen

in Fig. 8. A linear fit of the data provides the following

equation: s.s. partition = -13(3) ? 1.22(4) s.s. refinement

leading to a determination coefficient R2 of 0.990. It is

worth noting that excess s.s. is mainly taken up by the M2

site, as observed by Gianfagna et al. (2007). Such

systematic error could be possibly due to an imperfect

absorption correction as it has been consistently reported

from XRPD data collected in transmission mode.

Amphibole fibres morphology

An aliquot of each powdered sample, prepared for XRPD

analyses, was used to identify the amphibole fibre mor-

phology through TEM image analysis (see Appendix for

analytical details). In particular, the morphological features

(including also the crystal growth) of the amphibole

Table 4 Miscellaneous data of

the refinements, quantitative

phase analysis (QPA),

microstrain e0, and volume-

weighted mean column height

Lvol

Statistic indicators as defined in

Young (1993)

TB TB4a TB10b LIV335

Rwp 5.69 5.80 6.00 6.12

Rp 4.51 4.45 4.76 4.83

v2 1.12 1.10 1.10 1.17

DWd 1.66 1.66 1.70 1.52

Tremolite wt% 92.6(6) 100 90.2(5) 99.18(5)

Antigorite wt% 6.8(6) – – –

Quartz wt% 0.68(5) – 1.40(9) 0.82(5)

Albite wt% – – 7.8(4) –

Dolomite wt% – – 0.67(11) –

e0 0.0199(11) 0.046(4) 0.062(5) 0.0354(15)

Lvol (nm) 111(3) 106(9) 131(21) 66.0(18)

a (A) 9.84669(19) 9.8558(2) 9.8632(3) 9.8527(2)

b (A) 18.0632(4) 18.0869(4) 18.1059(5) 18.0920(4)

c (A) 5.27966(10) 5.28522(10) 5.29001(14) 5.29042(11)

b (�) 104.7388(16) 104.7266(16) 104.754(2) 104.7292(17)

volume (A3) 908.015(3) 911.20(3) 913.55(5) 912.06(4)

Fig. 7 Rietveld plots of sample

TB4a


123


particles having chemical composition consistent with

tremolite and/or actinolite have been considered. This

resulted in approximately 120 fibres characterised by an

aspect ratio [3:1.

All the analysed fibres have width exceeding 0.1 lm.

Fibres from samples TB10b and TB4a have aspect ratio

ranging from 5:1 to 9:1, whereas those from sample

LIV335 have aspect ratio smaller than 20:1, except for just

one fibre. The majority of fibres from sample TB have

aspect ratio spanning from 5:1 to 20:1. Only four fibres

have aspect ratio exceeding 20:1 with one reaching 100:1.

Those morphometric data have been plotted in a width vs.

aspect ratio diagram (Fig. 9). Most of the fibres, indepen-

dently on the aspect ratio, have widths smaller than 1 lm,

fitting with the asbestos criterion proposed by Harper et al.

(2008). Differently, whenever considering the asbestos

classification as proposed by Chatfield (2008), this diagram

shows that only four amphiboles from sample TB and one

amphibole from sample LIV335 fall within the region

delimiting the ‘‘asbestos’’. Finally, only one fibre belonging

Table 5 Selected bond

distances, site scattering (s.s.),

and polyhedral distortion D

(9104), defined as D ¼1n

PRi�R

R

� �2

where n is the

number of ligands, R is the

average bond length and Ri an

individual bond length (Brown

and Shannon 1973), of the four

amphibole samples

TB TB4a TB10b LIV335

M1-O192 2.073(10) 2.064(9) 2.069(12) 2.088(10)

M1-O2 92 2.099(9) 2.086(8) 2.092(12) 2.092(9)

M1-O3 92 2.056(8) 2.085(7) 2.091(10) 2.087(7)

\M1-O[ 2.076 2.078 2.084 2.089

D (9104) 0.73 0.24 0.26 0.01

s.s. (e-) M1 24.6(2) 28.7(2) 30.6(3) 31.4(2)

M2-O1 92 2.146(9) 2.158(8) 2.157(11) 2.147(9)

M2-O2 92 2.086(10) 2.091(9) 2.114(13) 2.074(10)

M2-O4 92 1.991(9) 2.022(8) 2.008(10) 2.013(8)

\M2-O[ 2.074 2.090 2.093 2.078

D (x 104) 9.46 7.06 8.95 6.95

s.s. (e-) M2 25.2(2) 27.8(2) 29.4(3) 29.8(2)

M3-O1 94 2.084(8) 2.097(7) 2.094(10) 2.111(8)

M3-O3 92 2.088(13) 2.062(12) 2.056(16) 2.052(12)

\M3-O[ 2.084 2.085 2.081 2.091

D (9104) 0.01 0.63 0.74 1.77

s.s. (e-) M3 12.66(17) 13.51(16) 14.8(2) 15.26(17)

\M1,M2,M3-O[ 2.079 2.085 2.086 2.086

s.s. (e-) M1 ? M2 ? M3 62.5(6) 70.0(6) 74.8(8) 76.4(6)

M4-O2 92 2.384(9) 2.358(8) 2.364(11) 2.366(9)

M4-O4 92 2.344(11) 2.321(9) 2.325(13) 2.332(10)

M4-O5 92 2.756(8) 2.797(7) 2.783(10) 2.774(8)

M4-O6 92 2.563(9) 2.560(8) 2.592(11) 2.583(9)

\M4-O[ 2.512 2.509 2.516 2.514

D (x 104) 42.50 57.06 53.97 50.40

s.s. (e-) M4 39.9(3) 39.7(3) 40.0(4) 39.2(3)

T1-O1 1.585(10) 1.582(9) 1.600(12) 1.594(9)

T1-O5 1.663(11) 1.624(10) 1.615(14) 1.629(11)

T1-O6 1.615(10) 1.632(9) 1.621(12) 1.632(9)

T1-O7 1.629(6) 1.627(5) 1.639(7) 1.636(6)

\T1-O[ 1.623 1.616 1.619 1.623

D (9104) 2.98 1.53 0.74 1.07

T2-O2 1.630(11) 1.663(9) 1.623(13) 1.642(10)

T2-O4 1.628(9) 1.600(8) 1.604(11) 1.593(9)

T2-O5 1.640(10) 1.643(9) 1.681(12) 1.665(9)

T2-O6 1.689(9) 1.668(10) 1.652(13) 1.651(10)

\T2-O[ 1.647 1.644 1.640 1.634

D (9104) 2.27 2.66 3.17 3.31


123


Table 6 Site partition (apfu), site scattering (s.s.), and mean cation radius as calculated from site partition (part.) and from refined bond distances

(ref.)

TB TB4a

apfu Radius part. Radius ref. s.s. (e-) part. s.s. (e-) ref. apfu Radius part. Radius ref. s.s. (e-) part. s.s. (e-) ref.

M1

Fe2? 0.02 0.22

Fe3? 0.04 0.08

Mg 1.94 1.70

Sum 2.00 0.719 0.716 24.72 24.6 (2) 2.00 0.724 0.718 28.20 28.7 (2)

M2

Fe2? 0.02 0.46

Fe3? 0.08 0.00

Mn2? 0.00 0.00

Mg 1.89 1.44

Cr3? 0.00 0.01

Ti4? 0.00 0.01VIAl 0.01 0.05

Sum 2.00 0.717 0.714 25.22 25.2 (2) 2.00 0.725 0.730 30.74 27.8 (2)

M3

Fe2? 0.07 0.11

Fe3? 0.00 0.00

Mg 0.93 0.89

Sum 1.00 0.724 0.725 12.84 12.66 (17) 1.00 0.727 0.725 13.54 13.5 (2)

M1 ? M2 ? M3 5.00 0.719 0.718 63.07 62.5 (6) 5.00 0.725 0.725 72.48 70.0 (6)

M4

Ca 1.93 1.87

Mn2? 0.02 0.05

Na 0.04 0.07

K 0.01 0.01

Sum 2.00 1.122 1.122 39.73 39.9 (3) 2.00 1.120 1.119 39.61 39.7 (3)

Fe2? 0.11 0.230 0.79 0.866

Fe3? 0.12 0.08

Mn2? 0.02 0.017 0.05 0.052

Mg 4.76 4.715 4.03 4.009

Cr3? 0.00 0.002 0.01 0.007

Ti4? 0.00 0.001 0.01 0.006VIAl 0.01 0.011 0.08 0.079IVAl 0.00 0.00

Ca 1.93 1.939 1.87 1.848

Na 0.04 0.037 0.07 0.070

K 0.01 0.007 0.01 0.009

Sum 7.00 6.959 7.00 6.946

TB10b LIV335


M1

Fe2? 0.34 0.46

Fe3? 0.05 0.08

Mg 1.61 1.46

Sum 2.00 0.728 0.724 29.46 30.6 (3) 2.00 0.731 0.729 31.56 31.4(2)

M2

Fe2? 0.75 0.61


123


to sample TB has morphological parameters matching the

asbestos identification criteria proposed by Berman and

Crump (2003).

In addition, the analytical procedure reported in Van Or-

den et al. (2008) has been applied to the same particles

having a chemical composition consistent to actinolite or

tremolite. The major fibre features for differentiating

asbestos amphiboles from non-asbestos amphiboles are

reported in Table 7. During the procedure, analysis of mor-

phological features (aspect ratio, width, shape of the fibre,

characteristics of the fibre sides and the fibre ends) attested

that most of the particles differentiate from asbestiform,

rather resembling elongate cleavage fragments (‘‘non-

asbestos’’ particles). In particular, fibres having smaller

aspect ratio (i.e. fibres from samples TB10b and TB4a) show

either irregular ends or curved/angular sides; the single fibre

from sample LIV335, previously classified as ‘‘asbestos’’ in

the Chatfield diagram, is characterised by an irregular shape

with a not constant diameter measured along the fibre length.

Amphibole fibres from samples TB show more homoge-

neous morphological characteristics, i.e. parallel sides, reg-

ular terminations, and straight shapes. Figure 10 shows a

representative TEM image, selected area electron diffraction

(SAED) pattern, and EDX spectrum for one of the four as-

bestiform amphiboles found in sample TB (Fig. 10a–c), in

comparison with representative TEM image, SAED pattern,

Table 6 continued

TB10b LIV335


Fe3? 0.00 0.08

Mn2? 0.00 0.00

Mg 1.08 1.14

Cr3? 0.01 0.00

Ti4? 0.00 0.00VIAl 0.16 0.17

Sum 2.00 0.727 0.733 34.78 29.4 (3) 2.00 0.720 0.718 33.83 29.8(2)

M3

Fe2? 0.15 0.24

Fe3? 0.05 0.00

Mg 0.80 0.76

Sum 1.00 0.725 0.721 14.80 14.8 (2) 1.00 0.734 0.731 15.36 15.3(2)

M1 ? M2 ? M3 5.00 0.727 0.726 79.04 74.8 (8) 5.00 0.728 0.726 80.75 76.4(6)

M4

Ca 1.82 1.84

Mn2? 0.03 0.00

Na 0.14 0.15

K 0.01 0.01

Sum 2.00 1.124 1.126 38.88 40.0 (4) 2.00 1.126 1.124 38.64 39.2(3)

Fe2? 1.24 1.340 1.31 1.469

Fe3? 0.10 0.16

Mn2? 0.03 0.025 0.00 0.000

Mg 3.49 3.491 3.36 3.353

Cr3? 0.01 0.008 0.00 0.000

Ti4? 0.00 0.004 0.00 0.003VIAl 0.16 0.278 0.17 0.308IVAl 0.12 0.14

Ca 1.82 1.821 1.84 1.810

Na 0.14 0.135 0.15 0.147

K 0.01 0.011 0.01 0.007

Sum 7.00 6.995a 7.00 6.959a

The M4 cation radius was calculated from the corresponding refined bond distance imposing a VIIIO radius of 1.36 Aa Plus 0.118 IVAl (sample TB10b) and 0.138 IVAl (sample LIV335)


123


and EDX spectrum for non-asbestiform amphibole particles

occurring in sample TB10b (Fig. 10d–f).

Discussion

Our data demonstrate that there is variability in the relevant

characteristics of amphibole passing from different litho-

types within an ophiolitic rock melange, encompassing the

range of different deformation structures in the field. This

variability concerns both the (1) crystal chemistry and (2)

morphology of the amphibole. (1) Actinolite amphibole is

widespread within the metagabbro fabric and within the

metamorphic veins (samples TB10b and LIV3435); both

actinolite and tremolite occur in chloritoschists (sample

TB4a), while tremolite occurs in serpentinites (sample TB).

(2) Actinolite in metagabbro shows fine-grained size and

prismatic-to-acicular morphology. Actinolite is always

associated with other minerals (albite and chlorite in par-

ticular), both along foliation and around the porphyroclasts,

without particular evidence for fibrous habit. Fibrous

actinolite is, on the other hand, concentrated within the

metamorphic veins as subordinate element to the plagio-

clase crystallisation. Fibres have aspect ratio ranging from

5:1 to 23:1 and they are confined within the metamorphic

veins, without propagation towards the surrounding meta-

gabbro foliation. Fibrous actinolite occurring along the

chloritoschist foliation has aspect ratio lower than 10:1. On

the other hand, tremolite fibres forming the metamorphic

foliation in serpentinites show the higher values (up to

100:1) for the aspect ratio.

Figure 11 summarises the in situ asbestos evaluation for

our case history using a qualitative bi-dimensional repre-

sentation of the geological heterogeneities deduced at the

field scale, integrated with inferences from laboratory

analyses. This conceptual sketch starts by correlating the

occurrence of fibrous amphibole with the geo-diversities of

the rock melange. This correlation assumes that the local

observations can be extrapolated to equivalent structures

and lithotypes recurrent in the region, whenever the geo-

logical conditions for rock formation (for example, the

tectono-metamorphic history) have been recognised as

operating uniformly overall the study area. The concen-

tration of fibrous amphibole has high probability values in

correspondence of serpentinites, chloritoschists, and

metamorphic veins, and decreases in correspondence of the

metagabbro mass. The critical step to the subsequent

determination of amphibole asbestos is the chemical–

morphological classification of the selected fibres that can

be best obtained by combining a multi-analytical approach.

Our interpretative reconstruction shows that the occurrence

of fibrous mineralisation may not univocally determine the

Table 7 Major fibre features for asbestos identification according to

analytical procedure by Van Orden et al. (2008)

Single crystal ‘‘True asbestos’’

Aspect ratio [5:1

Parallel sides yes

Perpendicular ends yes

Uniform diffraction contours yes

Selected area electron diffraction (SAED)

pattern

75� B angle B 90�

Twinning yes

Fig. 8 Comparison between the site scattering of the C group sites

from EMPA and that from the corresponding structure refinement.

Samples S1, S2, S3, S4 taken from Andreozzi et al. (2009), AS from

Pacella et al. (2008), and VS from Ballirano et al. (2008). Linear

regression, confidence (95 % level), and prediction intervals are

reported as full, dotted, and short dash lines, respectively

Fig. 9 Aspect ratio vs. width diagram for the analysed fibres. The

Chatfield (2008) field and the Berman and Crump (2003) field for

asbestiform particles are reported, as the 1 lm width criterion from

Harper et al. (2008). Note how the majority of particles can be

classified as asbestiform or non-asbestiform depending on the

criterion adopted


123


probability of the asbestos concentration in rock (Fig. 11).

On this ground, it is worth nothing that our results show

that only the tremolite crystals in serpentinite can be

classified as normative ‘‘asbestos’’ by the application of the

Van Orden et al. (2008) procedure, while amphibole fibres

from the other lithotypes/structures do not fit all the

properties for the ‘‘true asbestos’’. In this case, despite the

morphological similarities at the mesoscale, tremolite from

serpentinite and actinolite from metamorphic vein do not

give the same score of in situ asbestos hazard.

The results from this study can be generalised in two

main points: (1) importance of identifying the geological

conditions (protolith and deformation/mineralisation envi-

ronments) that catalyse the development of the fibrous

Fig. 10 TEM images (a and d), SAED patterns (b and e), and EDX spectra (c and f) for asbestiform amphibole from sample TB and non-

asbestiform amphibole from sample TB10b. The major fibre features for asbestos identification are listed in Table 7


123


mineralisation; and (2) the assessment of which fibrous

mineral can be really classified as normative asbestos.

1. In melange sequences, block lithotypes vary in size

(from few centimetres to several kilometres), in

distribution (they may be parallel or discordant to the

main tectonic features at the regional scale), and in

shape (they may appear as discontinuous, rootless

lenses wrapped by the country rocks). The identifica-

tion of different lithotypes is important for asbestos

detection purposes as certain rock units may have more

attitudes to encompass amphibole crystallisation than

others. Within the wide spectrum of ophiolitic rock-

types, the amphibole asbestos is mostly present in

gabbros, serpentinoschists, and various meta-sedimen-

tary rocks (e.g. Ross and Nolan 2003; Van Gosen

2007). In general, the bulk rock chemistry controls the

amphibole mineral chemistry during the progress of

the deformation-metamorphism in presence of external

silica-rich mineralising fluids (e.g. Evans 1977; Cart-

wright and Barnicoat 2003). Fibrous amphibole con-

centration in ophiolites is triggered by the chemical

disequilibrium occurring in strain environment of bulk

rock, such as within schistosity, fault surfaces, vein

network (Vignaroli et al. 2011 and references therein).

The geometrical properties (persistence, length, width,

spacing) of these deformation structures as well as

their orientation should be investigated in detail to

provide clues about the distribution of the fibrous

mineralisation in rocks.

2. There is not a univocal correspondence between the

fibres occurrence and assessment of normative asbes-

tos. Despite the relevance of fibrous morphology

detected at the field scale, not all fibres encounter the

properties (chemical, morphological, or both) of the

normative asbestos. Passing from the mesoscale to the

microscale is an imperative step within the identifica-

tion of asbestiform mineralisation, with respect to the

current normative. The integration of different miner-

alogical techniques (EMPA, XRPD) constrains the

chemical composition of the fibre bundles and the

single fibre. Observations at TEM reduce the ambigu-

ities in identifying the morphological and crystal

chemical properties of the single fibre for assessing

the real asbestos structure.

Anyway, the amphibole asbestos identification and

classification are still matter of ongoing debate (compare,

for example, Dodson et al. 2003 vs. Williams et al. 2013).

Classification methods dominantly based on the fibre

dimensional criteria (Berman and Crump 2003; Harper

et al. 2008; Chatfield 2008) do not provide univocal infor-

mation about the asbestos identification. A detailed evalu-

ation of the chemical and morphological parameters of the

fibrous minerals is thus needed. On the other hand, through

the combination of crystal chemical analysis and TEM

observations, the procedure proposed by Van Orden et al.

(2008) provides a more restrictive differentiation between

‘‘true asbestos’’ and ‘‘non-asbestos’’ cleavage fragments.

Further multidisciplinary studies (including epidemio-

logical ones) should be encouraged for supporting the

hypothesis that the most restrictive classification method

may be the safest in term of environment and health pro-

tection. At the present, the in situ asbestos hazard can be

associated to specific geological-structural sites where the

fibres show all chemical and morphological characteristics

for being classified as ‘‘true asbestos’’. The ‘‘true asbestos’’

definition remains subordinate to the selected counting

method for fibre.

Conclusions

This work outlines the importance to perform a multidis-

ciplinary, multi-analytical approach for evaluating the

in situ amphibole asbestos hazard in rock melanges affec-

ted by post-formation deformation structures. This evalu-

ation passes through the determination of the geological

features at the field scale and successive petrographic,

mineralogical and morphological laboratory analyses. The

effects of an appropriate, geological-based, approach have

Fig. 11 Qualitative schematization illustrating the probability of

asbestos concentration within the geo-diversities faced in the studied

ophiolitic suite


123


direct implication for all environments where disturbing

processes, either natural or anthropic in origin, of bulk rock

material produce and disperse airborne fibres and lead to

toxicity and consequent negative health effects.

Our results reveal that (1) the development of fibrous

mineralisation depends on several parameters during the

metamorphic evolution of the rock sequence, ranging from

strain, fluid activity, chemistry of the involved domain, (2)

a relationship between the field scale geological-structural

conditions and the in situ concentration of fibrous miner-

alisation can be documented, and (3) the evaluation of the

asbestos hazard is strongly affected by the fibre classifi-

cation method. Presently, the procedures for differentiating

the asbestiform and non-asbestiform fibres led to divergent

interpretations in assessing the potential environmental

impact in natural sites. A critical review of the analytical

protocols for asbestos counting method is needed, as nor-

matives regulating the asbestos hazard determination are

still controversial.

Acknowledgments The authors are grateful to M. Serracino and M.

Albano for the assistance at the electron microprobe and for SEM

investigations. We thank D.R. Van Orden and M.S. Sanchez for

helpful discussions and suggestions on the analytical procedures

adopted for the TEM analysis. The laboratory staff of the RJ Lee

Group Inc (Monroeville, PA, USA) is acknowledged for the assis-

tance in TEM analysis. The manuscript benefited of fruitful comments

and suggestions by three anonymous reviewers.

Appendix: experimental conditions for the laboratory

analyses

EMPA

The composition of the amphiboles was determined using a

Cameca SX50 electron microprobe equipped with five

wavelength-dispersive spectrometers using the following

conditions: 10 s counting time (peak), 5 s counting time

(background), beam diameter 2 lm, excitation voltage

15 kV, specimen current 15 nA. The following standards

were used: wollastonite (Si Ka and Ca Ka), rutile (Ti Ka),

corundum (Al Ka), magnetite (Fe Ka), metallic manganese

(Mn Ka), periclase (Mg Ka), orthoclase (K Ka), jadeite

(Na Ka), fluorophlogopite (F Ka), and sylvite (Cl Ka).

Raw data were corrected on-line for drift, dead time, and

background; matrix correction was performed with a

standard ZAF programme. Formulae were calculated on

the basis of O ? F?Cl = 24 apfu. Cations were assigned

to the B, C, and T group sites following Hawthorne (1981),

filled according to the order recommended by Leake et al.

(1997). Differently from several papers (Ballirano et al.

2008; Gianfagna et al. 2003, 2007; Pacella et al. 2008), no

Mossbauer spectroscopy was performed on the samples

because of the presence of other Fe-bearing silicates (an-

tigorite, chlorite) and iron oxides admixed with the fibres

as well as the presence of two admixed amphiboles in

sample TB4a. In fact, their occurrence would produce a

significant complication in data analysis rendering unreli-

able results with specific reference to site attribution.

However, an indirect Fe2?/Fe3? partition has been per-

formed following a procedure that will be described below.

X-ray powder diffraction (XRPD)

X-ray powder diffraction (XRPD) data were collected on

samples hand picked under a binocular that were ground with

a pestle, under ethanol, in an agate mortar. The corre-

sponding powders were loaded in 0.7-mm diameter boro-

silicate-glass capillaries that were subsequently aligned on a

standard goniometer head. Data were collected, using Cu Karadiation, on a parallel-beam Bruker AXS D8 Focus auto-

mated diffractometer operating in Debye-Scherrer geome-

try. It is fitted with Soller slits along both the incident and the

diffracted beam and a Peltier-cooled Si(Li) SolX detector.

Data were collected in the 5–155� 2h angular range, step size

0.02� 2h, and 40 s counting time.

Rietveld method

Diffraction data were evaluated by the Rietveld method

using TOPAS v. 4.2 (Bruker AXS, 2009). This programme

implements the Fundamental Parameters Approach FPA

(Cheary and Coelho, 1992). Such approach has been shown

to improve the quality of the fit as a result of a more

accurate description of the peak shape (Ballirano et al.

2009; Ballirano 2011a,b). Peak shape was modelled

through FPA imposing a simple axial model (14 mm) and

the size of the divergence (0.6 mm) and of the receiving

(0.2 mm) slits. Peak broadening was assumed to follow a

Lorentzian (size) and a Gaussian (strain) behaviour (Del-

hez et al. 1993). From evaluation of the integral breadths bi

of the individual reflections, microstructural parameters as

e0 microstrain (lattice strain), defined as bi = 4e0 tan h, and

volume-weighted mean column height Lvol, defined as

bi = k/Lvol cos h were extracted (Ballirano and Sadun,

2009). Absorption was refined following the formalism of

Sabine et al. (1998) for a cylindrical sample.

Starting fractional coordinates for amphiboles were

those of sample 93728 of Evans and Yang (1998). This

tremolite sample was characterised by an Mg/(Mg ? Fe2?)

ratio of 0.901 that is reasonably similar to that of all ana-

lysed samples. The isotropic displacement parameters were

set to the corresponding values calculated as the average of

the 20 samples of tremolite-actinolite-ferro-actinolite ana-

lysed by X-ray single crystal diffraction by Evans and

Yang (1998). Because of strong correlations with the site


123


occupancies they were kept fixed throughout the refine-

ments following the same approach used by Andreozzi

et al. (2009). No restraints on bond distances and angles

were imposed. Structural data for accessories phases were

taken from: Capitani and Mellini (2006) (antigorite), Lager

et al. (1982) (quartz), Meneghinello et al. (1999) (albite),

and Ross and Reeder (1992) (dolomite). As the only

detectable reflection of chlorite occurred at ca. 6� 2h, the

5–7� 2h angular range was removed from refinement of the

diffraction pattern of sample TB. Cell parameters were

refined for all phases, whereas fractional coordinates for all

atoms and site scattering for M(1), M(2), M(3), and M(4)

were also refined for the fibres. An attempt to detect the

occurrence of electron density at A, Am, and A2 failed in

keeping with none or small (\0.01 apfu) cationic excess at

M4 for all investigated samples.

Preferred orientation for amphiboles was modelled by

means of spherical harmonics (nine refinable parameters up

to the 8th order). Optimization of the spherical harmonics

terms produced a very marginal improvement of the fits, as

they were consistently found to be extremely small, as

expected for a capillary mount.

TEM

Samples were prepared for transmission electron micro-

scope (TEM) analysis by suspending a small portion of

each powdered samples in a beaker containing de-ionised

water. Each suspension was allowed to settle for 1 min

before removing an aliquot sample that was subsequently

filtered through a polycarbonate filter showing a porosity of

0.4 lm. The amount of the material was about 0.190 mg

for each dust samples on an effective filter area of

385 mm2 with a dilution factor of about 0.0001. The filter

area analysed for each sample was about 0.3336 mm2.

Filters were prepared and analysed for asbestos using

ASTM D5756-02 and Yamate et al. (1984) protocol to take

into consideration the structures having a minimum length

of 0.5 lm with an aspect ratio exceeding or equalling 3:1.

Analyses were carried out with a Jeol 1200 and a Jeol 2000

TEM, the latter equipped with an EDAX microanalysis.

Experimental conditions were as follow: acceleration

voltage was of 120 kV, magnification in the 10–20 kX

range, grid opening in the 10–25 lm range. The counting

method for identifying fibres on polycarbonate filters fol-

lowed the protocol in Yamate et al. (1984).

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