# Crystal harder than Sapphire?



## corght (Feb 26, 2012)

Is there watches with a crystal harder than Sapphire? The only logical choice would be synthetic diamond. Is there any watch out there with a diamond crystal? :-s


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## zeFiF (Mar 17, 2012)

hi,

check this : Mohs scale of mineral hardness - Wikipedia, the free encyclopedia


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## Wannaduck (Oct 21, 2009)

Can't get any better than Sapphire and Steel


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## corght (Feb 26, 2012)

zeFiF said:


> hi,
> 
> check this : Mohs scale of mineral hardness - Wikipedia, the free encyclopedia


Sapphire is a corundum, in the same family as Ruby. It's a crystalized aluminum oxide.


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## workaholic_ro (Dec 3, 2007)

Disambiguation from the perspective of a mining engineer:
Although useful, the article is a little confusing and incomplete. And so is the host (Wikipedia), but we still love it (at least as long as it's free).
In pure crystalline form 1,3,4,5,7,8,9,10 are clear and colourless. Calcite and feldpar are exceptions, calcite is clear but with a slight yellow tint and feldspar translucent or opaque.
The colour is given by very small amounts of impurities, usually metals. Sometimes, these metals also change the name of the minerals and so we have the variations: amethyst for the violet quartz, sapphire for the green corundum (can be blue, black or yellow too) and ruby for the red sapphire. Diamonds makes no exception, but keeping the original name. BTW, the most common colour of topaz is yellow and not blue.
Colourless sapphire is rare as a natural gem, therefore what we are used to call sapphire crystal in our watches is actually glorified synthetic corundum glass


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## WnS (Feb 20, 2011)

Transparent Silicon Carbide and Diamond are harder than Sapphire, and they can theoretically be used on watch crystals - probably too brittle and expensive for such a purpose though.


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## corght (Feb 26, 2012)

workaholic_ro said:


> Disambiguation from the perspective of a mining engineer:
> what we are used to call sapphire crystal in our watches is actually glorified synthetic corundum glass


Thnaks for the scientific explaination. So Calcite and feldpar are not crystals?


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## corght (Feb 26, 2012)

WnS said:


> Transparent Silicon Carbide


Hmm.. Silicon Carbide... I will search this material, seems interesting.


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## workaholic_ro (Dec 3, 2007)

corght said:


> Thnaks for the scientific explaination. So Calcite and feldpar are not crystals?


Mohs scale only applies to monomineralic crystalline forms. When I said exceptions I was talking about the colour.
No idea if there is any Moissanite (SiC) crystal of a size of a wristwatch, we need to investigate. But not the hardness is the subject to complain about sapphire, I don't think that scratches are very common. An unbreakable crystal rated with 9 on Mohs scale would be close to perfection.
BTW, just got an idea for a new thread


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## corght (Feb 26, 2012)

It's true that a hard material is sometimes brittle. The goal is to find a good compromise between hardness and strenght.


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## workaholic_ro (Dec 3, 2007)

After a short investigation the verdict for Moissanite (silicon carbide) is NO. Not for the price or mechanical properties, optical behaviour makes it improper for use as a watch crystal. It is strongly birefringent (double refractive). 
This is calcite, a different mineral, but the same story:







Unlike Moissanite, sapphire has a very low birefringence magnitude. The desired value is zero.
Theory and detailed explanation here.


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## WnS (Feb 20, 2011)

Nice work, that's the nail in the coffin for SiC. How about Boron Nitride?

http://en.wikipedia.org/wiki/Boron_nitride

Colourless and ~10 on the Mohs scale for C and W forms of the crystal.


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## slikmetalfab (Aug 17, 2011)

What about polycarb?
We currently use it for molding lenses on military helmets. With the special coating it makes them scratch resistant and small calibre bullet proof.

Its also uses the heads-up display for the inside of the helmets.

Scott

Sent from my DROID X2 using Tapatalk


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## corght (Feb 26, 2012)

That would be pretty impressive to say that your watch has a crystal of Boron Nitride!


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## Guest (Jun 10, 2012)

WnS said:


> Nice work, that's the nail in the coffin for SiC. How about Boron Nitride?
> 
> Boron nitride - Wikipedia, the free encyclopedia
> 
> Colourless and ~10 on the Mohs scale for C and W forms of the crystal.


IMHO, producing it, and make it really useable for a watch would eventually cost a lot of money.
Pros would be a small gain of hardness over corundum, cons would be availability, price and brittleness.


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## spain72 (Oct 27, 2010)

corght said:


> Is there watches with a crystal harder than Sapphire? The only logical choice would be synthetic diamond. Is there any watch out there with a diamond crystal? :-s


Hi. 
You can take a look at this thread I posted time ago.
I think you can find interesting information around.


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## WnS (Feb 20, 2011)

Misterpeter said:


> IMHO, producing it, and make it really useable for a watch would eventually cost a lot of money.
> Pros would be a small gain of hardness over corundum, cons would be availability, price and brittleness.


I'm sure a rich man, one who loves to pay for novelties, would love the idea. Another thing I'd like to see is a complete sapphire watch (case, bracelet and crystal) - that'd be a true skeleton watch.


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## Guest (Jun 18, 2012)

WnS said:


> I'm sure a rich man, one who loves to pay for novelties, would love the idea. Another thing I'd like to see is a complete sapphire watch (case, bracelet and crystal) - that'd be a true skeleton watch.


If you're so wealthy, ask Richard Mille then ;-)
Richard Mille RM 056 Chrono-Tourbillon Watch - Encased Entirely In Sapphire | FreshnessMag.com


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## WnS (Feb 20, 2011)

Misterpeter said:


> If you're so wealthy, ask Richard Mille then ;-)
> Richard Mille RM 056 Chrono-Tourbillon Watch - Encased Entirely In Sapphire | FreshnessMag.com


I'm neither wealthy, nor of poor taste.


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## Guest (Jun 18, 2012)

WnS said:


> I'm neither wealthy, nor of poor taste.


Sorry, I've misread it. You' re right, this watch has a ... questionable design :think:


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## WnS (Feb 20, 2011)

No need to be sorry. A poor person like me only believes he has better taste than a rich guy who can afford the ugly RM watch - to feel better about himself. I'm sure that if I was ridiculously wealthy I'd become eccentric and perhaps acquire a little megalomania, in which case, the ugly RM might become appealing.


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## corght (Feb 26, 2012)

Richard Mille are so expensive, it's insane.


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