Balangeroite

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Balangeroite
Specific gravity
2.96 - 3.10
Optical propertiesBiaxial -
Refractive indexnα = 1.680 nγ = 1.680
Birefringenceδ = 0.000
PleochroismDark brown and yellow brown parallel and perpendicular to [001]
References[2][3][4]

Balangeroite is found in one of the most important chrysotile mines in Europe, the Balangero Serpentinite. Hence, it is usually mistaken as an asbestiform in an assemblage of other mineral phases like chrysotile, magnetite and Fe-Ni alloys. However, Balangeroite does not lead to serious health problems caused by asbestos fibers.

Introduction

Balangeroite is classified as an inosilicate with 4-periodic single chains, Si4O12. It is a completely separate mineral from true asbestos. It is economically important for providing building materials, especially for thermal insulation purposes, fireproofing, etc.[5] Recent publications by Turci[6] have drawn some conclusions that balangeroite was not asbestos and had poor ecopersistence and biopersistence. This study also pointed out that it was the obvious chrysotile exposures there, not balangeroite, that caused the incidence of mesotheliomas.

Composition

The chemical formula for balangeroite is (Mg, Fe2+, Fe3+, Mn2+)42Si16O54(OH)40[7] and it has been calculated as shown in the diagram below by Compagnoni as follows:

Table 1a. Chemical analysis of balangeroite[7]
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,

oxidation of Fe2+ under heating.[7] 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[7]
(Mg 25.70 Fe2+7.69 Fe3+3.63 Mn2+1.65 Al0.17 Ca0.07 Cr0.01 Ti0.01) total = 38.93 Si15.38O53.66(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.[6] Balangeroite is isostructural to gageite.[7]

In contrast to chrysotile, however, balangeroite has more metal

amphiboles, may be easily removed.[6] As a consequence, the Mg and Fe are released forcing the silicate structure to become loosely bound and therefore pass into solution.[6] Further tests have been conducted on Balangeroite's ecopersistence and it showed fairly low eco-persistence at neutral pH.[6] Further studies were conducted by imitating weathering in an experiment to predict if weathered fibers retain the toxic potential present in freshly extracted fibers.[8] The tests proved that balangeroite showed the removal of Mg and Si, which shows continuous structural severance that extends far beyond the surface.[5]

Physical properties

Balangeroite can develop as loose fibers or be compact when in large volumes, which can be prismatic.[7] Antigorite flakes are included in relict prismatic balangeroite, while transmission electron microscopy observation shows that fibrous balangeroite is partially replaced by chrysotile.[9] The fibers run for a couple of centimeters in [001].

Geologic occurrences

The piemonte zone, remnant of the

metamorphic veins and in particular type 1 Vein that constitute relict prismatic balangeroite (often includes antigorite flakes) were formed during prograde high pressure metamorphism.[9] 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.[9]

Balangeroite was named after the location in which it was discovered.[7] 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.[7] This new mineral, balangeroite, was tested and found to be completely different from xylotile and metaxite in composition as well as optical properties.[7] Balangeroite was already discovered and a somewhat pure specimen was in the Turin University Mineralogy institute's museum since 1925, inventory no. 14873, labeled as "fibrous serpentine (asbestos)- San Vittore, Balangero".[7]

References

  1. S2CID 235729616
    .
  2. ^ Mindat.org
  3. ^ Webmineral.com
  4. ^ Handbook of Mineralogy
  5. ^
    ISBN 978-0-471-72157-4
    .
  6. ^
    PMID 19435981
    .
  7. ^ a b c d e f g h i j k l Compagnoni, Roberto; Ferraris G; Fiora L (1983). "Balangeroite, a new fibrous silicate related to Gageite from Balangero, Italy". American Mineralogist. 68: 214–29.
  8. S2CID 25489486
    .
  9. ^
    S2CID 32736985
    .

External links
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