1 hour ago, exchemist said:

I thought talc was sometimes classed as a clay mineral though. It too has sheets only bonded by van der Waals attraction, I think. With mica I think there is a cation between the sheets.

That's true.

In fairness both mica and talc occur more often as minerals in some rock eg granite.

The result of granite weathering creates many small mineral flakes that go twoards the clay soil.

The South West batholith granite is vey coarse grained which leads to easy breakdown and the fine china clays of Cornwall and coarser clays in Devon.

Somerset has a completely different geology with the sedimentary clays, sandstones and mudstones the result of run off from the edge of a former continental margin.

There are almost no igneous rocks in Somerset an exmoore is sedimentary, unlike Dartmoor, Bodmin and the other cornish moors.

Known examples of liquid fracture under gravity.

Now contrast this with the behaviour of separation drops (fractured water stream) from a dipping/slow running tap

Edited Monday at 07:38 PM1 day by studiot

18 hours ago, MigL said:

Granular solids can be made to act like liquids.
We regularly 'float' Sulphur prills, or flakes, on a cushion of N2 pressure, so it acts 'liquidy', and we can suck it under vacuum into a reactor for dithionation processes ( flakes need different N2 pressure than prills ) at my work.
This effect is also seen in avalanches and land-slides.

This is very interesting. Granules in any conglomerate are several orders of magnitude bigger than molecules, so this suggests that the surrounding processes, playing the role of a re-scaled 'solvent' perhaps? replicate what molecules would do in a fluid, only re-scaled.

Does that imply something like landslides being pictured as some kind of re-scaled phase change similar to what the original post by @paulsutton seemed to imply?

When I say 'solvant' I include air, water, the vacuum... The vacuum is a solvant, as far as any of us should be concerned.

2 hours ago, joigus said:

This is very interesting. Granules in any conglomerate are several orders of magnitude bigger than molecules, so this suggests that the surrounding processes, playing the role of a re-scaled 'solvent' perhaps? replicate what molecules would do in a fluid, only re-scaled.

Does that imply something like landslides being pictured as some kind of re-scaled phase change similar to what the original post by @paulsutton seemed to imply?

When I say 'solvant' I include air, water, the vacuum... The vacuum is a solvant, as far as any of us should be concerned.

With landslides, I am not sure, I think with an avalance (snow) the snow moves on a pocket of air, does a land slde do the same thing, we have had several in Dorset where the cliffs have collapsed, I generally think of a landside as also when thereis lots of water causing mud, and other debris to move down hill taking things with it.

I was thinking this, as we can pour liquids and also pour a container of Sodium Chloride into a beaker, despite the latter being made of small (granular) particles.

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

We have had this in Dorset,

https://www.bbc.co.uk/news/uk-england-dorset-68332305

However, I think these are caused by the area being very dry and collapsing (maybe weight related), the ground also cracks in very dry weather, ( probably the correct term is fissure )

Avalanches (IIRC) are moving snow but are these on top of a pocket of air or is there a sort of air pocket in front of the moving snow.

Does the shape of the particles also play a part, I think Salt (NaCl) is cuboid (or at least looking at the structure diagrams it is) graphite is layers so they slide, compared to diamond which is more ridged),

Sand appears to be trangular or perhaps pyramid shaped

https://chem.libretexts.org/Courses/Honolulu_Community_College/CHEM_100%3A_Chemistry_and_Society/14%3A_Earth/14.02%3A_Silicates_and_the_Shapes_of_Things

So maybe this is also a factor in how easy something will move around (even if sold).

Paul

41 minutes ago, paulsutton said:

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

Gravity plays a big part though, somehow analogous to the high stress that the authors of the paper mentioned for the case of fluids.

3 hours ago, paulsutton said:

I was thinking this, as we can pour liquids and also pour a container of Sodium Chloride into a beaker, despite the latter being made of small (granular) particles.

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

We have had this in Dorset,

https://www.bbc.co.uk/news/uk-england-dorset-68332305

However, I think these are caused by the area being very dry and collapsing (maybe weight related), the ground also cracks in very dry weather, ( probably the correct term is fissure )

Avalanches (IIRC) are moving snow but are these on top of a pocket of air or is there a sort of air pocket in front of the moving snow.

Does the shape of the particles also play a part, I think Salt (NaCl) is cuboid (or at least looking at the structure diagrams it is) graphite is layers so they slide, compared to diamond which is more ridged),

Sand appears to be trangular or perhaps pyramid shaped

https://chem.libretexts.org/Courses/Honolulu_Community_College/CHEM_100%3A_Chemistry_and_Society/14%3A_Earth/14.02%3A_Silicates_and_the_Shapes_of_Things

So maybe this is also a factor in how easy something will move around (even if sold).

Paul

If you want to understand all this, we need to start back 250 years before Christ, when a Greek gentleman made his famous utterance about Archimedes Principle.

The interesting thing is that the importance of AP, in this context, was not enunciated until after Relativity, after QM and after Godel in 1936 when Terzaghi introduced the notion of 'effective stress'.

So I am going to ask if you understand the notions of contact force, contact stress, and the classification into direct (also called normal) force and stress and (not indirect or abnormal) but tangential or shear force and shear stress,

Liquid mechanical behavious is controlled by shear stress, as is soil and rock mechanics in regard to failures such as landslip, avalanche, slope stability and so on.

Soils break due to shear failure in almost every case.

If you are not sure about any of the terms please ask and I will include the necessary explanations in my next post.

Conceptually it really is quite a simple subject ( mathematicians can always make it more hairy than it really needs to be)

1 hour ago, joigus said:

Gravity plays a big part though, somehow analogous to the high stress that the authors of the paper mentioned for the case of fluids.

High stress is just not necessary.

Did you manage to access the full paper by any chance ?

Edited 21 hours ago21 hr by studiot

7 minutes ago, studiot said:

High stress is just not necessary.

Did you manage to access the full paper by any chance ?

Unfortunately, no.

I didn't say it was necessary though. It could be sufficient. It could be neither: only highly correlative statistically. But any illuminating comments on your part are very welcome.

Think of two large diameter pistons face to face, with a liquid film bond between them. Air pressure on the external surfaces opposes rapid separation.

If the pistons are drawn apart slowly, the fluid pinches in at the circumference and gradually separates from the edge to the centre with no velocity discontinuity. The growing space between the separated films is occupied by air.

As more separation force is applied exceeding the sum of external pressure and van der Waals, the interface begins separating faster than air can fill the space, forming a vacuum and velocity discontinuity followed by a bang as the air catches up.

Generally the pressure within the film will dip below its vapour pressure and boil a bit reducing the degree of banginess (basis of cavitation).

Certain non-Newtonian fluids will like crystalline solids, support significant negative pressures in tension with consequent increased 'banginess'.

All I'm really seeing here are the underlying physics of Water Hammer and Liquid Column Separation

Tensile behaviour of elastic fluids covers some of the more polymery associated behaviours.