Asbestos

[StringJunky]

It appears that talc is magnesium silicate and some natural asbestos-types, are the same compound.  Is it the  physical structure, due to geological stresses,  that defines the difference?

Edited February 7, 2022 by StringJunky

[John Cuthber]

They are different materials.
Talc is a hydrated mag. silicate

Mg₃Si₄O₁₀(OH)₂
One formula given for amosite is Fe₇Si₈O₂₂(OH)₂

 crocidolite is Na₂Fe^I₃Fe^III₂Si₈O₂₂(OH)₂.

And so on...

[exchemist]

9 hours ago, StringJunky said:

It appears that talc is magnesium silicate and some natural asbestos-types, are the same compound.  Is it the  physical structure, due to geological stresses,  that defines the difference?

They have different composition, as @John Cuthberhas explained. My understanding is that the different physical appearance is due to the way the minerals cleave. Talc easily cleaves along a plane, in one dimension, into 2D sheets, rather as graphite and the micas do. Asbestos minerals cleave along two planes, more or less perpendicular to one another, resulting in 1D fibres. The behaviour depends on whether the crystal structure is in the form of sheets or chains of the silicate tetrahedra in the mineral.  

 

 

[joigus]

1 hour ago, John Cuthber said:

crocidolite is Na₂Fe^I₃Fe^III₂Si₈O₂₂(OH)₂.

It's II-oxidation number for ferrous iron, isn't it?

[chenbeier]

It has to be.

2*1+3*2+2*3+8*4 = 46 to 22*(-2)+2*(-1) = -46

 

[StringJunky]

Cheers chaps. I was trying to figure where the asbestos come from in talc. I had a read about the J&J litigation.

[exchemist]

9 minutes ago, StringJunky said:

Cheers chaps. I was trying to figure where the asbestos come from in talc. I had a read about the J&J litigation.

I gather they are often found together in nature (both metamorphic products of ultramafic minerals like olivine, I think), so measures have to be taken to ensure commercial talcum powder does not contain any asbestos. 

[StringJunky]

13 hours ago, exchemist said:

I gather they are often found together in nature (both metamorphic products of ultramafic minerals like olivine, I think), so measures have to be taken to ensure commercial talcum powder does not contain any asbestos. 

Cheers. The common one it seems found in talc that's fibrous is: "Anthophyllite is an amphibole mineral: Mg2Mg5Si8O22(OH)2" . What's with the Mg2Mg....in that formula, why not 3Mg....?

Edited February 8, 2022 by StringJunky

[chenbeier]

It should be Mg6Si₈O₂₂(OH)₂. in Comparison to Na₂Fe^I₃Fe^III₂Si₈O₂₂(OH)₂.

Edited February 8, 2022 by chenbeier

[StringJunky]

1 hour ago, chenbeier said:

It should be Mg6Si₈O₂₂(OH)₂. in Comparison to Na₂Fe^I₃Fe^III₂Si₈O₂₂(OH)₂.

Thanks

[chenbeier]

It is one Mg missing, it has to be  Mg₇Si₈O₂₂(OH)₂.

Edited February 8, 2022 by chenbeier

[exchemist]

9 hours ago, StringJunky said:

Cheers. The common one it seems found in talc that's fibrous is: "Anthophyllite is an amphibole mineral: Mg2Mg5Si8O22(OH)2" . What's with the Mg2Mg....in that formula, why not 3Mg....?

I think this indicates that Mg appears in 2 different sites in the lattice and can be partially replaced by other cations, such as Ca++ or Fe ++,  in the first position in related amphiboles. But I'm not 100% sure. The compositional ranges of these silicate minerals are not exact and are very complicated.  

[StringJunky]

From Wiki: "☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure."  Could that explain it?

I wouldn't like that in my lungs!

[exchemist]

57 minutes ago, StringJunky said:

From Wiki: "☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure."  Could that explain it?

I wouldn't like that in my lungs!

Yes I saw the square and the note too, but I'm not sure what it signifies. In the structure, I think there are both octahedral sites (6 coordination) and tetrahedral sites (4 coordination) for cations, which glue together anionic double chains of silicate tetrahedra. It may be that the Mg2 denotes occupancy of the tetrahedral and Mg5 occupancy of the octahedral sites in the lattice. Maybe the defect remark indicates a repeating gap (vacant site), necessitated by electric charge neutrality if all the cations are divalent. (There are some structures with monovalent cations, eg Na+, where more of these sites would be filled, I think.) But I"m guessing and unfortunately I can't find anything on the web that gives me a structure or explanation clear enough resolve the issue.

Maybe if we have a mineralogist on the forum he or she could interject. I am conscious that I am approaching the bullshit threshold. 

[studiot]

2 hours ago, StringJunky said:

I wouldn't like that in my lungs!

This article may interest you.

Quote

https://pubs.rsna.org/doi/10.1148/rg.261055070

Abstract

Pneumoconiosis may be classified as either fibrotic or nonfibrotic, according to the presence or absence of fibrosis. Silicosis, coal worker pneumoconiosis, asbestosis, berylliosis, and talcosis are examples of fibrotic pneumoconiosis. Siderosis, stannosis, and baritosis are nonfibrotic forms of pneumoconiosis that result from inhalation of iron oxide, tin oxide, and barium sulfate particles, respectively. In an individual who has a history of exposure to silica or coal dust, a finding of nodular or reticulonodular lesions at chest radiography or small nodules with a perilymphatic distribution at thin-section computed tomography (CT), with or without eggshell calcifications, is suggestive of silicosis or coal worker pneumoconiosis. Magnetic resonance imaging is helpful for distinguishing between progressive massive fibrosis and lung cancer. CT and histopathologic findings in asbestosis are similar to those in idiopathic pulmonary fibrosis, but the presence of asbestos bodies in histopathologic specimens is specific for the diagnosis of asbestosis. Giant cell interstitial pneumonia due to exposure to hard metals is classified as a fibrotic form of pneumoconiosis and appears on CT images as mixed ground-glass opacities and reticulation. Berylliosis simulates pulmonary sarcoidosis on CT images. CT findings in talcosis include small centrilobular and subpleural nodules or heterogeneous conglomerate masses that contain foci of high attenuation indicating talc deposition. Siderosis is nonfibrotic and is indicated by a CT finding of poorly defined centrilobular nodules or ground-glass opacities.