Atomic Composition Ratio of Amora Gem vs Natural Moissanite

#1
I had previously asked a few questions regarding the atomic composition of the Amora Gem on some other threads, but Less has advised to move it to this new dedicated thread. I just want to say I am no chemistry genius and hence why I was asking these questions :p In a recent post though Less has clarified the matter a bit which probably answers my question, but I'll post information here for others anyway.

Basically, from the Amora Gem description we know that the AG is atomically composed of 50% Silicon and 50% Carbon. We also know that the AG is a 4H SiC (Moissanite) polytype and that the Silicon Carbide family consists of ~250 crystalline forms. Less also mentions that all these Moissanite forms consist of 50% Silicon 50% Carbon.

My confusion came when I came across some data (here) on Moissanite and that it's composition ratio is 70% Silicon 30% Carbon. When I did some more digging I also came across some very interesting studies (links below) where natural Moissanite was discovered in Israel and when analysed, showed to have varying percentages of Carbon that exceeded the 30% ratio mentioned in the data above. It varied from +2% to +12% (so 32 to 42 percent Carbon).

So a few questions I had at the end of the day was, is the ratio of lab-made Moissanite different to natural Moissanite whereby you can control exactly 50:50 ratio? And so has all lab-made Moissanite, 6H and 4H, always been created at that 50:50 ratio, or is it what makes AG better than other Moissanite vendors (for e.g others could create 70:30 etc I dunno if it's cheaper, or more efficient)?

Here are some of the links

Moissanite Mineral Data

http://www.shefayamim.com/ufksa7390/Moissanite Properties and Terrestrial Occurrence 02082016(1).pdf

http://www.shefayamim.com/uploadimages/image/Abstract_2009.pdf

http://www.shefayamim.com/uploadimages/image/SY_poster_2009.pdf
 
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talk-admin

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#2
I see the confusion here - they are referring to weight % composition and not atomic % composition.

When they talk about 70:30 ratio, it's because they are measuring samples by atomic weight.

In other words, break down a sample and analyze the weight of each element involved.
Carbon = 12 weight atomically
Silicon = 28 weight atomically

1 Carbon + 1 Silicon = 28 + 12 = 40 total.
Thus, Silicon % by weight = 28/40 = .7 ratio to total weight, or 70% Silicon, 30% Carbon - by weight.

When I or others talk about 1:1 or 50:50 ratio of Carbon to Silicon, I mean atom to atom ratio (atomic composition) and not weight composition.

Structurally you have to have 1 Carbon and 1 Silicon to make any type of Silicon Carbide or 50% Carbon, 50% Silicon. The differences then are the stacking order and bond types.

Now, the 1:1 is the ideal but many growers have
1 - less sophisticated equipment (PVT style growth) or
2 - simply growth processes optimized for bulk/volume production and not ultra-pure,

and so commonly end up 'overstuffing' carbon into the crystal and this can result in a less brilliant crystal as there is 'interstitial' carbon or carbon hanging out in between the crystal lattice.

It's not bonded so the lattice is still 1:1 ratio for bonded atoms, but you have unwanted trapped carbon throughout the crystal overall which will reduce the optics. In the extreme this creates the classic black carbon spots but is more commonly just a darker look to it as your eyes aren't going to be able to detect the excess atoms, but do note the overall effect in terms of reduced total brilliance.

It has been noted that our Amora Eternity compared to the F1 is clearer/brighter for example and the moissanite from India or other places are notably not as clear/bright.
Some of that is from cutting of course but inherently it's also affected by the crystal purity and perfection as well, with interstitial carbon being the most common purity problem.

i.e.
Aggregation of carbon interstitials in silicon carbide: A theoretical study
"Based on the calculated formation energies, the complex formation of carbon interstitials or their aggregation to carbon antisites is energetically favored in SiC. "

Phys. Rev. B 68, 125201 (2003) - Aggregation of carbon interstitials in silicon carbide: A theoretical study

Hope that helps,
Less
 
#3
What's heavier?

A pound of feathers or a pound of steel?


;)


What's interesting to note here about atomic weight is, that although silicon is much heavier per volume than carbon, a diamond is heavier the SiC per volume by a small %
 
#4
I see the confusion here - they are referring to weight % composition and not atomic % composition.

When they talk about 70:30 ratio, it's because they are measuring samples by atomic weight.

In other words, break down a sample and analyze the weight of each element involved.
Carbon = 12 weight atomically
Silicon = 28 weight atomically

1 Carbon + 1 Silicon = 28 + 12 = 40 total.
Thus, Silicon % by weight = 28/40 = .7 ratio to total weight, or 70% Silicon, 30% Carbon - by weight.

When I or others talk about 1:1 or 50:50 ratio of Carbon to Silicon, I mean atom to atom ratio (atomic composition) and not weight composition.

Structurally you have to have 1 Carbon and 1 Silicon to make any type of Silicon Carbide or 50% Carbon, 50% Silicon. The differences then are the stacking order and bond types.

Now, the 1:1 is the ideal but many growers have
1 - less sophisticated equipment (PVT style growth) or
2 - simply growth processes optimized for bulk/volume production and not ultra-pure,

and so commonly end up 'overstuffing' carbon into the crystal and this can result in a less brilliant crystal as there is 'interstitial' carbon or carbon hanging out in between the crystal lattice.

It's not bonded so the lattice is still 1:1 ratio for bonded atoms, but you have unwanted trapped carbon throughout the crystal overall which will reduce the optics. In the extreme this creates the classic black carbon spots but is more commonly just a darker look to it as your eyes aren't going to be able to detect the excess atoms, but do note the overall effect in terms of reduced total brilliance.

It has been noted that our Amora Eternity compared to the F1 is clearer/brighter for example and the moissanite from India or other places are notably not as clear/bright.
Some of that is from cutting of course but inherently it's also affected by the crystal purity and perfection as well, with interstitial carbon being the most common purity problem.

i.e.
Aggregation of carbon interstitials in silicon carbide: A theoretical study
"Based on the calculated formation energies, the complex formation of carbon interstitials or their aggregation to carbon antisites is energetically favored in SiC. "

Phys. Rev. B 68, 125201 (2003) - Aggregation of carbon interstitials in silicon carbide: A theoretical study

Hope that helps,
Less
Hi Less,

I have been poking around your website for a few hours and as someone with a technical background I appreciate the trove of technical details that you provide.

That said, I am confused at this apparent contradiction found on the Amora gem description page:
Amora H&A gem compared to other gems:

  • More brilliant than moissanite (Amora GEM is a different crystal with superior optical properties than moissanite). Amora Gem is the most brilliant gem anywhere.
  • 27% harder than sapphire
  • More brilliant than cubic zirconia
  • Harder than cubic zirconia
The bolded portion seems to contradict other information that both amora and moissanite are SiC D4H crystals. Is amora simply the result of a process that grows a more pure version of this crystal or is it in fact a different structure?

edit: found out that less already answered this question on quora. tl/dr is that the atoms are configured the same but the dimensions are different, resulting in a different bandgap. Thanks for all the info :)

Amora Gem and Moissanite are two different crystals that have similar composition, but are different due to having different crystal structures (polytypes or polymorphs). Both are members of the “SiC” (Silicon Carbide) family which encompasses over 200+ members. Thus, there is no single “SiC” crystal as your question implies…but rather a huge family of over 200+ of them.

The simple answer to your question though is that Amora has a higher band gap than Moissanite and is thus truly colorless, and has a slightly higher refractive index (brilliance) than Moissanite. Dispersion (fire) still needs to be measured and we hope to have GIA help with that in the next month or two but it looks to have higher fire than Moissanite based on the degree of hexagonality:cubic ratio vs Moissanite.

To elaborate - All members of the SiC (Silicon Carbide) family have a common composition - all members are made of Silicon and Carbon.

All members differ however in their crystal structure. Cubic Moissanite, Amora Gem, Moissanite, 2H, Rhombohedral SiC etc. all vary in their stacking sequence of the layer of carbon/silicon, and type and degree of crystal habit - hexagonal vs cubic structure (or rhombohedral structure, etc) as they arrange the layers differently.

An analogy - both graphite and diamond are primarily carbon…yet having a different crystal structure results in very different physical and optical properties.

All materials in the universe have properties that are unique based on

a)what atoms they are composed of (composition) and

b)how those atoms are arranged.

Change a, b, or both and you have different physical, chemical and optical properties.

The SiC crystal originally marketed as moissanite suffered from a lower bandgap, or a weaker ability to tightly bond it’s electrons. This meant it could never be a truly colorless gem because some portion of the higher energy blue light was moving it’s electrons and being absorbed. Hence all the issues with yellow or green tinting, K/L/M color grades, etc. and why Charles and Colvard insisted for a long time it couldn’t be graded on the GIA diamond scale (b/c it was not near colorless as claimed…).

I worked hard to bring Amora Gem to reality because, like diamond, the Amora polytype had a much tighter electron binding (or bandgap) and thus like diamond, could be natively a truly colorless gem (up to D color) and with more fire and brilliance than diamond (and moissanite). Effectively a crystal that could be the ultimate gem.

As a crystal, it is harder and slower to grow than Moissanite and thus more expensive.

(There is some confusion now because this past year or so Charles and Colvard later changed their underlying SiC crystal to one that was also colorless, but continue to label it Moissanite… so depending what ‘version’ of Moissanite you are in fact getting one of two distinctly different types of SiC, with differing color and optical properties while still being publicly labeled as Moissanite).

Regardless, the net is Amora Gem has superior fire and brilliance compared to diamond and can be truly colorless (up to D color). Original moissanite could not achieve similar color grading due to weakness in it’s crystal structure and did not have as much fire/brilliance as Amora Gem.
 
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