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Harder than diamond, softer than talc
  
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Tom Mazanec




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PostPosted: Dec 18, 2016 17:32    Post subject: Harder than diamond, softer than talc  

I know diamond is as hard as nature gets, but are there any synthetics which rival or exceed it in hardness/
Are any solid minerals softer than talc (which Mohs presumably overlooked)?
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rocks2dust




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PostPosted: Dec 18, 2016 18:33    Post subject: Re: Harder than diamond, softer than talc  

Some materials like lonsdaleite/fullerite diamond and wurtzite boron nitride are theoretically harder than Mohs 10, but meteoric and synthesized examples thus far have had defects in their lattice structures that cause them in practical tests to show softer than normal diamond.

There are elements (e.g., Cesium) that are softer than talc, but I'm not sure whether any occur naturally in pure crystalline/mineral forms.
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Dale Hallmark




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PostPosted: Dec 18, 2016 19:39    Post subject: Re: Harder than diamond, softer than talc  

How technical do you want to be? Ice, technically a mineral, can be a range of hardness and can potentially be softer than 1 but it is typically listed as a hardness of 1.5.

Can't think of anything softer that is truly a mineral. Some ex minerals of course, such as oxides like Ochre, and maybe some chalks, etc., can be softer. But they are not minerals.

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John Betts




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PostPosted: Dec 18, 2016 20:02    Post subject: Re: Harder than diamond, softer than talc  

Fullerenes (C60) are harder than diamond.
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Pete Richards
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PostPosted: Dec 18, 2016 20:58    Post subject: Re: Harder than diamond, softer than talc  

An interesting question is whether fullerines are minerals or not. Minerals have specific crystal structures. Crystal structures are three-dimensional and extend indefinitely. Fullerine molecules are either finite (C60) or one-dimensionally infinite - tubes; I'm not aware of any that form infinite sheets or 3-D structures of C-C bonds.

Of course, you could make a solid of buckyballs stacked together in some closest-packed array, but then the properties of the "mineral" would be those of the stacked structure (weak!!!!) not those of the individual fullerine molecules (strong!!!).

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Dale Hallmark




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PostPosted: Dec 18, 2016 22:33    Post subject: Re: Harder than diamond, softer than talc  

But then Buckyballs would be man made.
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Volkmar Stingl




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PostPosted: Dec 19, 2016 01:07    Post subject: Re: Harder than diamond, softer than talc  

Pete Richards wrote:
An interesting question is whether fullerines are minerals or not. Minerals have specific crystal structures. Crystal structures are three-dimensional and extend indefinitely. Fullerine molecules are either finite (C60) or one-dimensionally infinite - tubes; I'm not aware of any that form infinite sheets or 3-D structures of C-C bonds.

Of course, you could make a solid of buckyballs stacked together in some closest-packed array, but then the properties of the "mineral" would be those of the stacked structure (weak!!!!) not those of the individual fullerine molecules (strong!!!).


A mineral is defined also by its natural occurrence, which excludes man-made fullerenes.
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lluis




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PostPosted: Dec 19, 2016 03:40    Post subject: Re: Harder than diamond, softer than talc  

Well, it is said that in shungite there are fullerenes.

http://www.mindat.org/min-11040.html

Then, fullerenes could be natural occurring.

Whether they are a true mineral or not, well, what Peter said makes me think that they are not. Or that they are not harder than diamond....

With best wishes

Lluís
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CranCowan




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PostPosted: Dec 19, 2016 06:24    Post subject: Re: Harder than diamond, softer than talc  

This sounds a bit like a riddle. The best answer I can think of are carbon based minerals or mineraloids. Graphite might be softer than talc if it contained enough water and q-carbon is supposed to be harder than diamond:
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lluis




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PostPosted: Dec 19, 2016 07:01    Post subject: Re: Harder than diamond, softer than talc  

But, CranCowan. then you forget that question is about minerals.

q-Carbon is man made, and a graphite with water is not a mineral, just an impure graphite....

For man made substances, both can be placed easily...

With best wishes

Lluís
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CranCowan




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PostPosted: Dec 19, 2016 07:35    Post subject: Re: Harder than diamond, softer than talc  

lluis wrote:
But, CranCowan. then you forget that question is about minerals.

q-Carbon is man made, and a graphite with water is not a mineral, just an impure graphite....

For man made substances, both can be placed easily...

With best wishes

Lluís


Not really. Q-carbon is a mineraloid (like obsidian) and although it has not been found in nature yet, one can't assume that it's not there. Until recently fullerenes were also considered man-made, but they have been found in fulgurites and orbiting stars.

Ironically, the only examples of pure minerals are generally man-made. Nature's minerals almost always contain impurities.

The general definition of mineral (according to Wiki) says it needs to be solid at room temperature which excludes water and mercury. But that is a bit arbitrary in my opinion. The rest of the universe is not at room temperature.
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lluis




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PostPosted: Dec 19, 2016 10:30    Post subject: Re: Harder than diamond, softer than talc  

Hi, CranCowan

Well, what I found is q-Carbon is man made. Maybe I missed something, and by sure that I do know it before you mention it (my fault!)
But if you take a look at this link, you will see what I say

https://www.extremetech.com/extreme/219186-q-carbon-is-harder-than-diamond-incredibly-simple-to-make
(link normalized by FMF)

On the other side, fullerenes were first man made, and then, it is reported that are found in shungite.

Fullerenes are found, and q-Carbon is still under research. A difference. And they could or could not be found. As was said, synthetic compounds harder than diamond exist, although not found in nature. So, no minerals. At least till yet. Well, maybe fullerene, if you disregard what Peter said, that I think is the *point*.

As to what you said about "rest of universe is not at room temperature".

Agreed. But definitions are definitions, and to enter in kingdom of possibilities is, being soft, quite in-concrete.

With best wishes

Lluís
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lluis




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PostPosted: Dec 19, 2016 10:38    Post subject: Re: Harder than diamond, softer than talc  

Hi, all

Many thanks to CranCrowan (any name? to talk to a nickname makes me feel crazy.....)
Looking in the theme, permitted me found that there is a natural material, mineral, that is harder than diamond (it is said about 58% harder...)

https://www.newscientist.com/article/dn16610-diamond-no-longer-natures-hardest-material/
(link normalized by FMF)

So, ...

With best wishes

Lluís
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