Mineralogical Asbestos Assessment in the Southern Apennines ( Italy ) : A Review

This paper deals with petrography and mineralogy of serpentinitic rocks occurring in the Southern Apennines (Italy) with the aim to review the already available literature data and furnish new details on asbestos minerals present in the studied area. Two sites of Southern Italy were taken into account: the Pollino Massif, at the Calabrian-Lucanian border, and the surroundings of the Gimigliano and Mt. Reventino areas where serpentinites of Frido Unit are mainly exposed. Textural and mineralogical features of the studied rocks point to a similar composition for both sites including asbestos minerals such as chrysotile and tremolite-actinolite series mineral phases. Only in the Pollino Massif serpentinites edenite crystals have been detected as well; they are documented here for the first time. This amphibole forms as fibrous and/or prismatic crystals in aggregates associated with serpentine, pyroxene, and calcite. Metamorphism and/or metasomatic alteration of serpentinites are the most probable processes promoting the edenite formation in the Southern Apennine ophiolitic rocks.


Introduction
In the last decade, many researchers have focused on serpentinites cropping out in the ophiolitic sequences and have aimed to assess and monitor their potential as asbestos-bearing lithotypes, since asbestos occurrence in mafic and ultramafic rocks that undergo ocean floor metamorphism is relatively common [1][2][3][4].In Italy, the occurrence of these rocks is documented both in the Alps and Apennines.These outcrops extend from the Ligurian-Piedmont through the Tuscan-Emilian Apennines as far as Val Tiberina and continue, in disjointed groupings, to the Calabrian-Lucanian Apennines [5].
As is known, the definition of asbestos used by regulatory agencies [6] for identification includes the following six mineral species: chrysotile, crocidolite, tremolite, actinolite, amosite, and anthophyllite [7].Among these minerals, only chrysotile is a sheet silicate; the other minerals are included within the amphibole supergroup.Silicate minerals belonging to the serpentine and amphibole groups are flexible, heat-resistant, and chemically inert.These minerals usually occur with an elongated and/or bladed prismatic habit, although they may be acicular or fibrous as well.In the European countries, fibers having a length ≥5 µm, a width <3 µm, and an aspect ratio >3 are defined as "asbestos" by Directive 2003/18/CE.
Asbestos is classified as a carcinogen material of Category 1 by the world health authorities [8].Several authors ascribe the fibers' toxicity to their morphology and size, chemical-physical Fibers 2019, 7, 24 2 of 13 characteristics, surface reactivity, and biopersistence [9].It is known that the presence of impurities (i.e., Fe, Ni, and Ti) in the ideal chemical composition in asbestos fibers, even in small amounts, affects their chemical and physical properties, size, and shape [10][11][12][13].Moreover, according to in vitro studies on biological-system-mineral interactions, both characteristics (impurities and size) are considered to be responsible for its pathological effects [14,15].
In this paper, we present data related to petrography and mineralogy of serpentinites in representative sites at the Pollino Massif (Calabrian-Lucanian boundary) and Gimigliano-Mt.Reventino (Sila Piccola, Northern Calabria), with the principal aim to review the main modes of occurrence of asbestos minerals in the Southern Apennines.

Ophiolitic Sequences in Southern Italy
The Southern Apennines is a fold-and-thrust chain developed between the Upper Oligocene and the Quaternary during the convergence between the African and European plates [16][17][18].The ophiolitic sequences incorporated in the Southern Apennine chain are related to the northwest subduction of the oceanic lithosphere pertaining to the Ligurian sector (divided in the Frido Unit and North Calabrian Unit) of the Jurassic Western Tethys.They crop out in the northeastern slope of the Pollino Ridge, along with the Calabria-Lucanian border zone, and in the Gimigliano-Mt.Reventino Unit (Sila Piccola, Southern Italy) (Figure 2).At the Calabrian-Lucanian boundary, the investigated sites are on well-exposed outcrops along road cuts, active and inactive quarries or in the proximity of villages (Pietrapica quarry, Timpa Castello quarry, Fagosa quarry, and Fosso Arcangelo, San Severino Lucano, Rovine Convento Sagittale localities, Mt.Nandiniello and Ghiaia quarry) (Figure 1), whereas close to the Gimigliano town the outcrops are in correspondence of quarries at Sila Piccola, Northern Calabria [5,[19][20][21].

Analytical Methods
In this paper, we report and discuss data available in literature referring to the petrographical and mineralogical studies performed on serpentinites from selected sites of southern Apennines.In  In the following sections, details on geological setting and formations of both sites are presented.
In the Pollino Massif, the serpentinite rocks are cataclastic and massive.Cataclastic serpentinites show a high degree of fracturing and deformation.The millimeter to centimeter fractures are almost filled by exposed white and grey fibrous minerals [30,32,33].Fibers occur as both large and elongate minerals developed over slickensided surfaces and/or as very fine-grained phases pervading the whole rock.Massive serpentinites show a low fracturing and deformation without exposed fibers.

The Gimigliano-Mt. Reventino Serpentinites
The Gimigliano-Mt.Reventino (Sila Piccola, Figure 2) occurs in the northern sector of the Calabrian-Peloritan Orogen [43,44].According to Ogniben [45,46], the Northern Calabria sector consists of three main tectonic complexes: the Apennine Units Complex, at the bottom, made up of Mesozoic sedimentary and metasedimentary terranes; the allochthonous Alpine Liguride Complex, in the intermediate position, consisting of a series of Cretaceous-Paleogene metamorphic units that include metapelites, ophiolites, and carbonates; the Calabride Complex, at the top, with granites, gneisses, and metasedimentary deposits derived from Hercynian and pre-Hercynian terranes.The Mt. Reventino area is characterized mainly by lenses of metabasalts and serpentinites limited by low angle tectonic systems, with metapelites, metalimestones, and metarenites of uncertain ages of the Frido Unit (Liguride Complex).The massive-banded metabasalts and serpentinites lenses constitute the upper part of Mt.Reventino [43].In the ophiolitic bodies, ascribed to the Liguride Complex of oceanic derivation [46][47][48][49], the serpentinites occupy the cores of the major tight folds and are partially or completely surrounded by isolated bodies of metabasalts and subordinate metadolerites [43].In the Gimigliano-Mt.Reventino two different types of serpentinites occur as foliated and massive rocks.Mostly dark green serpentinites crop out as massive bodies that only sometimes are weakly foliated and cut by serpentine and calcite veins [5,[19][20][21].
the upper part of Mt.Reventino [43].In the ophiolitic bodies, ascribed to the Liguride Complex of oceanic derivation [46][47][48][49], the serpentinites occupy the cores of the major tight folds and are partially or completely surrounded by isolated bodies of metabasalts and subordinate metadolerites [43].In the Gimigliano-Mt.Reventino two different types of serpentinites occur as foliated and massive rocks.Mostly dark green serpentinites crop out as massive bodies that only sometimes are weakly foliated and cut by serpentine and calcite veins [5,[19][20][21].

Analytical Methods
In this paper, we report and discuss data available in literature referring to the petrographical and mineralogical studies performed on serpentinites from selected sites of southern Apennines.In particular, data here presented are from Dichicco et al. [32,33], Punturo et al. [19], Bloise et al. [5], and Campopiano et al. [20].
The petrographic characterization was carried out by optical microscopy on thin sections of rock samples.Percentages for fibrous minerals have been calculated by means of point-counting modal analysis following the EPA/600/R93-116 method.The mineralogical compositions have been obtained Fibers 2019, 7, 24 5 of 13 by using X-ray diffraction (XRD) on bulk rock powder.Specific analyses on single minerals were performed by µ-Raman spectroscopy, FT-IR spectroscopy, SEM-EDS, and electron microprobe (EMP) analyses.Details of analytical conditions are reported in the following papers: Dichicco et al. [32,33], Punturo et al. [19], and Bloise et al. [5].

Asbestos Minerals in Serpentinites from the Pollino Massif
Serpentinites are characterized by an original pseudomorphic texture and mylonitic-cataclastic structures (Table 1).They are made up of fibrous minerals accounting for the 55% of the total mineral composition.The mineralogical assemblage consists of serpentine group minerals, amphibole minerals (mainly tremolite-actinolite series), titanite, clinopyroxene, clinochlore, magnetite, Cr-spinel, talc, quartz, and carbonate phases.The serpentinites are cross-cut by a micro-network of nanometer to millimeter veins filled by fibrous serpentine and serpentine ± amphiboles, amphibole minerals, and calcite ± amphiboles [32].Chrysotile occurs as short and fine-fibers in the matrix and in the contact between vein and rock.Chrysotile occurs preferentially in serpentinites that have undergone some degree of recrystallization, in which the serpentine minerals have developed interlocking microstructures.Primary magmatic clinopyroxene occurs in partially preserved grains.The amphibole shows acicular, fibrous, and elongated habitus and forms in veins and/or in the rock matrix as crowns around the clinopyroxene porphyroclasts [32].Serpentine group minerals were also identified by µ-Raman spectroscopy.Chrysotile is distinguished from the other minerals of the serpentine group by means of an antisymmetric band at about 3699 cm −1 , with a tail toward lower wavenumbers, and a less pronounced peak at about 3691 cm −1 [32].As reported by Dichicco et al. [32,33], different types of amphibole minerals also occur in the analyzed rocks.In the µ-Raman spectra of the OH vibrational region, the amphibole shows Fibers 2019, 7, 24 two peaks, the most intense of which is at 3675-3673 cm −1 (Mg; Mg; Mg), the second most intense at 3660-3663 cm −1 (Mg; Mg; Fe).The number and relative intensity of these bands represent pure tremolite and almost pure tremolite with a small percentage of Fe 2+ (Fe-tremolite).The presence of Fe 2+ is confirmed by FT-IR [33].No Fe 3+ is present, owing to the absence of absorption bands at ∆ = 50 cm −1 from the tremolite reference band in the FT-IR spectrum [33,[52][53][54][55][56].
Secondary Electron observations by ESEM analyses show asbestos tremolite fibers that are straight, flexible and approximately 100 µm in length.The EDS chemical analysis shows that amphibole crystals are homogeneous, without zoning, although some crystals display different amounts of SiO 2 , CaO, MgO, Fe 2 O 3 , Al 2 O 3 , and Na 2 O in the rim and core [33].
The microchemical composition of most amphiboles detected by EMPA is typical of Ca-amphiboles, including tremolite and Mg-Fe-hornblende (Table 3) [56].
In addition, the EMP analysis revealed for the first time the presence of edenite in the serpentinites rocks of the Frido Unit.As shown in Figure 3, in the serpentinites of the Pollino Massif, edenite crystals grow with a fibrous habitus and form aggregates often associated with serpentine, diopside, and calcite.

Asbestos Minerals in Serpentinites from Gimigliano-Mt. Reventino
The serpentinites show remnants of the original protogranular texture, which is inherited from their harzburgitic-lherzolitic protoliths [5,19].The mineral assemblage is made of serpentine group minerals and magnetite ± tremolite-actinolite ± chlorite ± clinopyroxene ± Cr-spinel, and calcite [5,19] (Table 1).The serpentine group minerals, together with small magnetite grains, completely replaced the original olivine and orthopyroxene crystals that appear as pseudomorphic aggregates showing typical net-like and mesh textures [5,19].According to Punturo et al. [19], clinopyroxene is in the rarely preserved holly-leaf shaped Cr-spinels that, in most cases, are quite completely retrogressed to magnetite and chlorite.Different vein systems, filled by serpentine group minerals, cross-cut the rock.In general, serpentine fibers may be oriented either perpendicular to the vein selvages ("cross" serpentine) or according to their elongation directions ("lamellar" serpentine).Minor calcite and talc flake aggregates or actinolite-tremolite fibers may occur within the serpentine matrix.
The X-ray diffraction analysis revealed that these rocks are mainly constituted of serpentine group minerals, followed by chlorite and tremolite [5,19] (Table 2).Calcite was detected less frequently and in low amounts.μ-Raman spectroscopy identified chrysotile, lizardite, and antigorite.In the spectral region associated with the structural bending characterization, serpentine group minerals are characterized by very similar μ-Raman spectra.In chrysotile, the characteristic ν5 (e) bending vibrations of the SiO4 tetrahedra are shown at 388 and 344 cm -1 .Lizardite shows a very similar pattern to chrysotile [5], whereas antigorite displays a characteristic band occurring at 1042 cm -1 and an intense band at 683 cm -1 .The two bands observed at 378 and 634 cm -1 appear to be slightly shifted when compared with the same vibrations present in the chrysotile spectrum [5].Similarly to the serpentinites of the Pollino Massif, the tremolite of Gimigliano-Mt.Reventino rocks is characterized by the presence only of Fe 2+ detected by FT-IR analysis [57].The Fe 3+ presence is excluded because of the absence of the absorption bands at Δ = −50 cm −1 .Further, the FT-IR and SEM-EDS analyses confirmed the presence of antigorite, chrysotile, and fibrous minerals, from the tremolite-actinolite series, in the samples from Mt. Reventino [20,21,58].Results of the EMP analysis performed on selected fibrous crystals of edenite are shown in Table 4. Major element compositional range of this amphibole is as follows: SiO 2 = 51.264-54.293wt%, CaO = 23.64-25.507wt%, MgO = 16.332-17.680wt%, Al 2 O 3 = 0.259-2.709wt%, and FeO tot = 1.257-2.852wt% [57].In addition, in the edenite crystals, low amounts of several trace elements, such as Mn, Cr, and Ni, are also present.

Asbestos Minerals in Serpentinites from Gimigliano-Mt. Reventino
The serpentinites show remnants of the original protogranular texture, which is inherited from their harzburgitic-lherzolitic protoliths [5,19].The mineral assemblage is made of serpentine group minerals and magnetite ± tremolite-actinolite ± chlorite ± clinopyroxene ± Cr-spinel, and calcite [5,19] (Table 1).The serpentine group minerals, together with small magnetite grains, completely replaced the original olivine and orthopyroxene crystals that appear as pseudomorphic aggregates showing typical net-like and mesh textures [5,19].According to Punturo et al. [19], clinopyroxene is in the rarely preserved holly-leaf shaped Cr-spinels that, in most cases, are quite completely retrogressed to magnetite and chlorite.Different vein systems, filled by serpentine group minerals, cross-cut the rock.In general, serpentine fibers may be oriented either perpendicular to the vein selvages ("cross" serpentine) or according to their elongation directions ("lamellar" serpentine).Minor calcite and talc flake aggregates or actinolite-tremolite fibers may occur within the serpentine matrix.The X-ray diffraction analysis revealed that these rocks are mainly constituted of serpentine group minerals, followed by chlorite and tremolite [5,19] (Table 2).Calcite was detected less frequently and in low amounts.µ-Raman spectroscopy identified chrysotile, lizardite, and antigorite.In the spectral region associated with the structural bending characterization, serpentine group minerals are characterized by very similar µ-Raman spectra.In chrysotile, the characteristic ν5 (e) bending vibrations of the SiO 4 tetrahedra are shown at 388 and 344 cm -1 .Lizardite shows a very similar pattern to chrysotile [5], whereas antigorite displays a characteristic band occurring at 1042 cm -1 and an intense band at 683 cm -1 .The two bands observed at 378 and 634 cm -1 appear to be slightly shifted when compared with the same vibrations present in the chrysotile spectrum [5].Similarly to the serpentinites of the Pollino Massif, the tremolite of Gimigliano-Mt.Reventino rocks is characterized by the presence only of Fe 2+ detected by FT-IR analysis [57].The Fe 3+ presence is excluded because of the absence of the absorption bands at ∆ = −50 cm −1 .Further, the FT-IR and SEM-EDS analyses confirmed the presence of antigorite, chrysotile, and fibrous minerals, from the tremolite-actinolite series, in the samples from Mt. Reventino [20,21,58].

Discussion and Conclusions
Data presented in this study display a very similar mineralogical composition for both the considered serpentinites including serpentine group minerals, amphiboles, pyroxene, chlorite, talc, titanite, magnetite, and carbonates.However, compared to the serpentinites from Northern Calabria, the Pollino Massif serpentinites are characterized also by the presence of quartz, dolomite, and edenite.
Based on textural and mineralogical data, quartz and dolomite are always found in association with, talc likely suggesting their formation during a metasomatic event.According to Boschi et al. [59], in fact, serpentine minerals may easily alter to talc + dolomite assemblage as the following reaction: Instead, quartz may be thought as the result of the direct precipitation from migrating fluids that, as stated by Moore and Rymer [60], may become enriched with dissolved silica during the alteration of serpentine and other primary silicates of mafic and ultramafic rocks.
As regards edenite, the presence of such a mineral within the serpentinitic rocks from the ophiolitic sequence of Southern Apennines is documented here for the first time.Edenite is a double chain silicate mineral of the amphibole group with the following general formula: NaCa 2 (Mg,Fe) 5 [Si 7 AlO 22 ](OH) 2 [61].This is a rare mineral in the ophiolitic sequences although its presence has been documented in the oceanic serpentinites from the Mid-Atlantic Ridge and the Greater Antilles (Cuba, Dominican Republic) [62,63], where it testifies a medium to high metamorphism.As suggested by Bucher and Frey [64], the edenite formation is linked to the greenschist-amphibolite facies transition.In particular, such a mineral is produced by albite-consuming reactions in volcanic rocks, as albite + tremolite = edenite + 4 quartz, or in basic rocks, as olivine + labradorite + H 2 O = ortopyroxene + edenite + spinel [61], and occurs during metamorphic events that promote systematic changes of the amphibole composition (from tremolite to edenite).
However, metasomatic processes not correlated to metamorphism can also be responsible for the formation of edenite or (more commonly) fluoro-edenite crystals.The F-edenite of Biancavilla, a village located in the etnean volcanic complex of Eastern Sicily (Southern Italy), is an example of an amphibole not metamorphic in origin.According to Comba et al. [65], the Sicilian F-edenite is found in voids and fractures of the benmoreitic lava covering the Mt.Calvario or in highly weathered pyroclastic products and scoriae that have been involved by metasomatizing hot fluids during volcanism or processes linked to it.
Regardless of process promoting edenite formation, it is worth noting that this amphibole, similarly to the more common asbestos minerals, may crystallize with fibrous habit and thus could

Figure 1 .
Figure 1.Geological sketch map of the Southern Apennines-Calabria-Peloritani chain and location of the study areas (modified after [50]).

Figure 2 .
Figure 2. Geological sketch map of the Southern Apennines-Calabria-Peloritani chain and location of the study areas (modified after [50]).

Table 3 .
Chemistry of selected fibrous tremolite and Mg-Fe-hornblende crystals in the serpentinites of the Pollino Massif.

Table 4 .
Chemistry of selected fibrous edenite crystals in serpentinites samples from the Pollino Massif.