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What exactly is asbestos?
Posted: Sat Aug 21, 2021 9:31 pm
by nezumi
Yes it's a fibrous silicate (white, brown, blue, yadda ya) and it causes mesothelioma (the cancer my Gran has) but what. exactly. is. it?
Re: What exactly is asbestos?
Posted: Sat Aug 21, 2021 11:47 pm
by Pishwish
The following is a massive simplification and may not be entirely correct as I was never very good at mineralogy. Geologists need to learn it though because it is fundamental to learning about igneous rocks.
You know the way that organic chemistry is based on connecting carbon to other carbons, hydrogens and other functional groups along tetrahedral bonds?
Silicate chemistry is is a bit like that, but the basic units are SiO
4 tetrahedra not individual carbon atoms.
If the SiO
4 tetrahedra in a mineral are connected to cations and not to other tetrahedra, the mineral belongs to the island silicate group. Olivine is the best known example.
If the SiO
4 tetrahedra in a mineral are connected, sharing O atoms on either side, the mineral belongs to the chain silicate group. There are single chain minerals called pyroxenes and double chain minerals called amphiboles.
If the SiO
4 tetrahedra in a mineral share O atoms on more than 2 sides, forming sheets, the mineral belongs to the sheet silicate group. These are the mica minerals.
If the SiO
4 tetrahedra in a mineral share all their O atoms with other tetrahedra in a 3-D framework, the mineral belongs to the framework silicate group. These include quartz and feldspar.
Now these structures do not always translate to the macro level, but the amphiboles have 2 planes of weakness and can split into elongated forms, the micas have one plane of weakness and like to break into thin sheets, and quartz does not have a plane of weakness. (This is sort of analogous to polymers, graphite, and diamond).
Asbestos minerals are mainly amphiboles. Amphiboles are common, but only a few are asbestiform. Chrysotile (white asbestos) is a type of sheet silicate, though.
Re: What exactly is asbestos?
Posted: Sat Aug 21, 2021 11:50 pm
by basementer
It's a family of naturally occurring minerals that forms long thin crystals. There are half a dozen of them. Somewhat fibrous and very inert and fire resistant, the fibre from the minerals was(and I think still is) processed for use as additives in various products such as cement tile, roofing panels*, textured paint, fireproofing materials including clothing. The damage the fine fibres cause in the lungs is not because it's toxic in the way that, say, mercury is, but it causes mechanical damage to the fine structures in the lung, resulting in inflammation and scarring.
* That's where I encountered it - a summer job sweeping up asbestos debris in the 1970s. Fingers crossed, no problems yet.
Re: What exactly is asbestos?
Posted: Sun Aug 22, 2021 8:46 am
by Gfamily
Pishwish wrote: Sat Aug 21, 2021 11:47 pm
The following is a massive simplification and may not be entirely correct as I was never very good at mineralogy. Geologists need to learn it though because it is fundamental to learning about igneous rocks.
You know the way that organic chemistry is based on connecting carbon to other carbons, hydrogens and other functional groups along tetrahedral bonds?
Silicate chemistry is is a bit like that, but the basic units are SiO
4 tetrahedra not individual carbon atoms.
If the SiO
4 tetrahedra in a mineral are connected to cations and not to other tetrahedra, the mineral belongs to the island silicate group. Olivine is the best known example.
If the SiO
4 tetrahedra in a mineral are connected, sharing O atoms on either side, the mineral belongs to the chain silicate group. There are single chain minerals called pyroxenes and double chain minerals called amphiboles.
If the SiO
4 tetrahedra in a mineral share O atoms on more than 2 sides, forming sheets, the mineral belongs to the sheet silicate group. These are the mica minerals.
If the SiO
4 tetrahedra in a mineral share all their O atoms with other tetrahedra in a 3-D framework, the mineral belongs to the framework silicate group. These include quartz and feldspar.
Now these structures do not always translate to the macro level, but the amphiboles have 2 planes of weakness and can split into elongated forms, the micas have one plane of weakness and like to break into thin sheets, and quartz does not have a plane of weakness. (This is sort of analogous to polymers, graphite, and diamond).
Asbestos minerals are mainly amphiboles. Amphiboles are common, but only a few are asbestiform. Chrysotile (white asbestos) is a type of sheet silicate, though.
That's really useful, what
and why.
Thanks
Re: What exactly is asbestos?
Posted: Sun Aug 22, 2021 11:13 am
by nezumi
Thank you Pishwish - exactly the right level of complexity. Now I understand a bit better!
Re: What exactly is asbestos?
Posted: Sun Aug 22, 2021 12:00 pm
by veravista
Just reminded me of Nonza Beach in Corsica. Beautiful location but very black because of the asbestos pollution from the now disused mine. Never seen it crowded for some reason...
Re: What exactly is asbestos?
Posted: Sun Aug 22, 2021 3:41 pm
by Grumble
basementer wrote: Sat Aug 21, 2021 11:50 pm
and I think still is
It certainly is, Russia and China use it with gay abandon, the way we used it before we realised it could do nasty stuff to your lungs.
Re: What exactly is asbestos?
Posted: Mon Aug 23, 2021 6:21 pm
by Stupidosaurus
I once read that asbestos causes cancer because epithelial cells strongly adhere to the long fibres and the resulting extension in their size and surface area promotes carcinogenesis somehow, possibly by the shape change driving abnormalities in cell division? I can't remember the reference. There is no minimum carcinogenic dose of fibres, so inhaling a single fibre could lead to cancer.