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Mineralogically , What is Asbestos and How D oes it Form?

Mineralogically , What is Asbestos and How D oes it Form?. A.E. Williams-Jones. Department of Earth and Planetary Sciences McGill University, Montreal, Canada. What is Asbestos ?.

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Mineralogically , What is Asbestos and How D oes it Form?

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  1. Mineralogically, What is Asbestos and How Does it Form? A.E. Williams-Jones Department of Earth and Planetary Sciences McGill University, Montreal, Canada

  2. What is Asbestos? Asbestos is a mineral that crystallises in some rocks to form fibres. These fibres are commonly less that 1 micron in diameter, and may be > 5 cm long Chrysotile Tremolite

  3. Asbestos Relative to the Human Hair Amosite asbestos fibres as viewed with a scanning electron microscope Human hair

  4. Types of Asbestos Six type of asbestos have been recognized, but mineralogically they fall into two classes, serpentine (90%) and amphibole (10%) Serpentine Class Amphibole Class Chrysotile (1) Riebeckite (crocidolite) (2) Anthophyllite(3) Grunerite-cumminmgtonite(4) (amosite) Tremolite-actinolite (5-6)

  5. Serpentine Class Serpentine forms at spreading centres as a result of hydration of the Earth’s mantle via reactions of the type: 3Mg2SiO4 + 4H2O + SiO2aq Mg6Si4O10(OH)8) Olivine Serpentine Spreading Centre at Mid-ocean Ridge Seawater is drawn down into lithospheric mantle Oceanic crust Lithospheric Mantle Asthenospheric Mantle

  6. Serpentine Class The serpentine is exposed in ophiolites, which represent oceanic crust and mantle, that has been obducted onto the continent. Quebec produced most of this asbestos (chrysotile). Continent Oceanic crust Mantle Ophiolite Erosion Continent Mantle

  7. Asbestos vein formation Serpentine is normally a platy mineral and only becomes asbestiform when it grows in extensional veins Rock mass pulled apart undergoes brittle failure, fractures form and fibres grow from the two faces of the fracture . Chrysotile Serpentinite Serpentinite

  8. The Serpentine Class – Sheet Silicates • Silicon tetrahedra bond to each other to form a negatively charged sheet • Sheets are bonded ionically by cations (Mg2+) in octahedral co-ordination Si4O10-4 Serpentine OH- Mg6Si4O10(OH)8

  9. Lizardite and Chrysotile Chrysotile is the asbestiform variety of the serpentine group mineral lizardite(Mg6Si4O10(OH)8), which is a sheet silicate Lizardite sheets in a serpentinite

  10. Serpentinisation Mantle olivine (Mg2SiO4) is hydrated to form lizardite (Mg6Si4O10(OH)8) Experimental alteration of olivine to lizardite Lizardite sheets rolling to form proto-chrysotile Normand et al. (2002)

  11. The Transformation of Lizarditeto Chrysotile High resolution transmitted electron microscope image showing lizardite (Lz) partly transformed to chrysotile (C)

  12. The Structure of Chrysotile The octahedral and tetrahedral layers, which are planar in lizardite, are concentrically distributed in chrysotile to form cylinders within cylinders that are weakly held together by van der Waals forces

  13. High Resolution TEM Images of Chrysotile Note the concentric cylinders of octahedral and tetrahedral layers loosely held together by hydrogen bonding Lizardite sector fibre Evans et al. (2013)

  14. Banded Iron Formation and Asbestos Oxygenation of the oceans and atmosphere by cyanobacteria lead to oxidation of soluble Fe2+ to insoluble Fe3+ producing banded iron formation (BIF) Fe3O4, Fe2O3, SiO2 FeCO3

  15. Metamorphism of BIF Produces Crocidoliteand Amosite Fe3O4 + 8SiO2 + 4FeCO3 + H2O (Fe)7Si8O22(OH)2 + 4CO2 + ½O2 Magnetite Quartz Siderite Grunerite (Amosite) 3Fe3O4 + 8SiO2 + 2H2O + 2Na+ Na2Fe2+3Fe3+2Si8O22(OH)2 + 2F2O3 +2H+ Magnetite Quartz Riebeckite (Crocidolite) Hematite) Crocidolite) Hot magma releases heat and fluids

  16. The Structure of Amphibole Double chain silicates with the general formula AB2C5Si8O22(OH)2 Si4O11-6 Riebeckite (Na2(Fe2+,Fe3+)Si8O22(OH)2, Tremolite (Ca2Mg5Si8O22(OH)2, Anthophyllite (Mg,Fe)2(Mg,Fe)5Si8O22(OH)2 Cummingtonite-Grunerite (Ditto) OH- Na+, Ca2+, Mg2+, Fe2+ Si4O11-6

  17. The Structure of Amphibole

  18. Tremolite in Chrysotile Deposits Diorite dykes interact with serpentinite to produce rind of tremolite 5Mg6Si4O10(OH)8 + 12Ca2+ + 28SiO2 6Ca2Mg5Si8O22(OH)2+ 24H+ + 2H2O Serpentinite Tremolite Diorite Diorite

  19. The contradiction of Québec chrysotile mines Québec chrysotilemines contain less than 1% tremolite but the lungs of diseased workers from these mines contain more tremolite than chrysotile. Why? Nayebzadehet al. (2001)

  20. A Possible Explanation for the Tremolite Anomaly The structure of chrysotile, a rolled sheet silicate, is intrinsically unstable enabling it to dissolve more easily in lung fluids than tremolite The calculated rates of dissolution of chrysotile and tremolite in synthetic lung fluid Tremolite Chrysotile Wood et al. (2006)

  21. Thank you

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