Hellenica World

Balangeroite

Balangeroite is found in one of the most important Chrysotile mines in Europe, the Balangero Serpentinite. It is considered an asbestiform in an assemblage of other mineral phases like Chrysotile, Magnetite and Fe-Ni Alloys. In addition to its fibrous occurrence, Balangeroite’s association with Chrysotile raises concerns about its potential toxicity when its fibers are inhaled.

Introduction

Balangeroite is classified as belonging to one of the two asbestiform silicate groups, the Serpentine group. It is intergrown with the dominant member of the serpentinite, Chrysotile[1] , often associated with tremolite (a contaminant of Chrysotile), which is classified as part of the Amphibole group, the other asbestiform silicate Massive serpentines are economically important for providing building material. The fibrous nature of Chrysotile is particularly valuable for thermal insulation purposes, fire proofing etc [2] Tremolite contaminated Chrysotile shows that the toxicity of the asbestos is due to the presence of Tremolite and not the entire mass of the Chrysotile [3]. Recent publications by Turci [3] have drawn some conclusions that Balangeroite contaminated Chrysotile does have some areas of concern and can be attributed to the overall toxicity of the airborne fibers in the Balangero mine. Therefore, it cannot be compared to tremolite or croidolite in level of pathogenicity as the two have been proven by autopsies and biopsies to be present in the bodies of the people exposed to their fibers.

Composition

The chemical formula for Balangeroite is (Mg, Fe²⁺, Fe ³⁺, Mn²⁺) 42 Si16 O54 (OH) 40 [1] and it has been calculated as shown in the diagram below by Compagnoni as follows:

Table 1a. Chemical Analysis of Balangeroite [1]
SiO2 28.37
TiO2 0.03
Al2O3 0.27
Fe2O3 8.89
Cr2O3 0.03
FeO 16.95
MnO 3.59
MgO 31.81
CaO 0.13
H2O 9.93
Total 100.00

Wet Chemical, X-ray Fluorescence and electron microprobe analysis were used to deduce the composition of Balangeroite [1]. The common intergrowth with Chrysotile proved to be valuable in providing better chemical resolution as portrayed in table 1. The results varied due to submicroscopic intergrowths or zoning. From the wet chemical analysis, there was 9.5% average weight loss after calcination at 1000oC, due to the presence of water [1]. This was calculated as the difference from 100% of microprobe results, with the assumption that large quantities of material usually contain some impurities, and the possible oxidation of Fe2+ under heating [1]. A ratio of Fe2+/Fe3+ = 2.12 was obtained and on the basis of the known volume and density, the empirical formula for the unit cell was derived [1] (Mg25.70 Fe2+7.69 Fe3+3.63 Mn2+1.65 Al0.17 Ca 0.07 Cr0.01Ti0.01)total =38.93Si15.38 O53.66 (OH)35.92.

Structure

Balangeroite is based on an octahedral build that consists of channels that are filled by chains of silicate tetrahedra grouped in three and 4 rows running along the fiber axis [3]. Balangeroite is isostructural to Gageite [1].

In contrast to Chrysotile, however, Balangeroite has more metal ions than Silicon ions and might be in some cases seen as complex Iron Oxide containing some type of silicate structure in its framework [3]. The surrounding fluid takes in a large number of the cations which are octahedrally coordinated, which unlike amphiboles, may be easily removed [3]. As a consequence, the Mg and Fe are released forcing the silicate structure to become loosely bound and therefore pass into solution [3]. Further tests have been conducted on Balangeroite’s ecopersistence and it showed fairly low eco-persistence at neutral pH [3]. Further studies were conducted by imitating weathering in an experiment to predict if weathered fibers retain the toxic potential present in freshly extracted fibers [2]. The tests proved that Balangeroite showed removal of Mg and Si which shows a continuous structural severance which extends far beyond the surface [2].

Physical properties

Balangeroite can develop as loose fibers or compact when in large volumes which can be prismatic [1]. Antigorite flakes are included in relict prismatic Balangeroite, while TEM observation shows that fibrous Balangeroite is partially replaced by Chrysotile [4]. The fibers run a couple of centimeters in the [001].

Table 2. Physical Properties of Balangeroite [1].
Chemical Formula (Mg, Fe²⁺, Fe ³⁺, Mn²⁺) 42 Si16 O54 (OH) 40
Crystal Data Monoclinic, 2/m point group, elongated along [001]
Color Pleichroism; dark brown and yellow brown parallel and perpendicular to [001] successively
Opacity Transparent only in thin sections
Cleavage One or more {hk0} are very good
Tenacity Brittle, hardness is not determined (n.d)
Luster Vitreous- greasy
Optical Class Biaxial (-), due to its isostructural nature with gageite, it should be biaxial but due to its texture, it only has 1 refractive index.
Space group P2/n
Density 2.98 g/cm3 measure on a torsion balance


Geologic occurrences

The piemonte zone, remnant of the Piemontese Ocean from the late Jurassic, is home to the majority of the serpentines of the Western Alps. Balangero mine is located in the Lanzu Ultramafic Massif which is in the inner part of the piemonte zone [4]. The Lanzu Ultramafic Massif is believed to have been involved in the subduction processes that were affiliated with the closure of the Piemontese Ocean in the late Jurassic [4]. The earliest generation of metamorphic veins and in particular type 1 Vein that constitute relict prismatic Balangeroite (often includes antigorite flakes) were formed during prograde high pressure metamorphism [4]. Fibrous Balangeroite is limited to the serpentine-infested rim of the northern Lanzu Ultramafic Massif, with its abundance in the inactive Balangero asbestos mine, where it was discovered [4]. Balangeroite was named after the location in which it was discovered [1]. It was brought to the attention of Robert Compagnoni and his colleagues at the Universitia Della Calabria, Cosenza Italy by a mineral collector, and Enrico Beccuti in 1977 [1]. Mine workers at the Balangero mine had first discovered it and named it, based on its overall color and fibrous nature of other minerals present in the mine, Xylotile or Metaxite [1]. This new mineral Balangeroite was tested and found to be completely different from Xylotile and Metaxite in composition as well as optical properties [1]. Turns out that Balangeroite was already discovered and a somewhat pure specimen was in Turin University Mineralogy institute’s museum since 1925, inventory no. 14873, labeled as “ fibrous serpentine (asbestos)- San Vittore, Balangero” [1].

Literature survey

The most highly cited paper on Balangeroite in the web of science was Robert Compagnoni and colleagues’ for “ Balangeroite, A new fibrous silicate related to Gageite from Balangero, Italy” with twenty five citations. Authors of other articles, most often with Robert Compagnoni as co-author, often cite this article in further research of the mineral and other minerals related to it. Due to its asbestiform nature it has been cited by Francesco Turci (2005) and colleagues in the Journal of toxicology and Environmental Health “Potential Toxicity of no regulated asbestiform minerals: Balangeroite from the Western Alps”

Further investigation

Asbestiform minerals are gaining attention in the news and are of great concerns due to the potential health threat their fibers pose when inhaled. Klein and Duttrow [2] chronicle that the regulatory bodies classify asbestiform minerals as having the same effects in both mines as well as in office buildings etc. This has resulted in the banning of Chrysotile mining in the United States due to health concerns of those exposed to asbestos [2]. The intergrowth of Chrysotile with Balangeroite has become controversial as a result. Tests have been performed by Francesco Turci [5] show that Balangeroite fibers have the ability to produce oxidative stress, and is therefore a determinant in their genotoxic effects. Crocidolite’s fibers, an amphibole riebeckite, according to Klein and Duttrow [2] pose a greater health hazard especially in Mesothelioma cases. The concerns about the toxicity of Balangeroite are especially seen among health organizations within governments. Mineralogists, however, even with concerns about the health hazard Balangeroite might pose, are skeptical about calling it a cancer- inducing asbestiform as various experiments were performed on Balangeroite, show that it cannot be largely responsible for the health effects found in humans. Balangeroite research has been going on since it was discovered in 1983 but due to its intergrowth with chrysotile, it is very difficult to find a pure sample in large enough quantities for additional testing in order to get less controversial results. The contaminants in Balangeroite cause it to yield differing results which in turn give rise to controversies as is the case with its potential lethality regarding lung cancer and Mesothelioma.

References

1. ^ a b c d e f g h i j k l m n o Compagnoni, Roberto; Ferraris G and Fiora L (1983). "Balangeroite, a new fibrous silicate related to Gageite from Balangero, Italy". American Mineralogist 68: 214–29.
2. ^ a b c d e f Klein, Cornelius; Barbara Duttrow (2008). "19". in Ryan Flahive. The Manual of Mineral Science (23rd ed.). John Wiley & Sons, Inc.. pp. 515–520. ISBN 978-0-471-72157-4.
3. ^ a b c d e f g Turci, Francesco; Tomatis M and Compagnoni R, et al (2009). "The Role of Associated Mineral Fibers in Chrysotile Asbestos Health effects: The Case of Balangeroite". Annals of Occupational Hygiene 53: 491–497.
4. ^ a b c d e Groppo, C; Tomatis M, Turci F, et al (2005). "The Potential Toxicity of Non-Regulated Asbestiform Minerals: Balangeroite from the Western Alps Part 1: Identification and Characterization.". Journal of Toxicology and Environmental Health- Part A- Current Issues 68: 1–19.
5. ^ Turci, Francesco; Tomatis M, Gazzano E, et al (2005). "The Potential Toxicity of Non-Regulated Asbestiform minerals: Balangeroite from the Western Alps Part 2: Oxidant Activity of Fibers.". Journal of Toxicology and Environmental Health-Part A- Current Issues 68: 21–39.

External links

* Handbook of Mineralogy's entry on balangeroite
* Webmineral.com
* Entry on Mineraldata.com
* Entry on Mindat.org


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