Franklin Faceters Frolic 10 (FFF10) July 27, 28 & 29 at The Factory Franklin, NC
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sat Jul 22, 2017 10:45 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 13 posts ] 
Author Message
 Post subject: Ways to make synthetic corundum?
PostPosted: Wed Apr 12, 2017 3:52 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1092
Location: Central Queensland, Australia
I came across the school's mineral specimen kit yesterday. It is tiny and uninteresting and I think the kids will be much more interested in the specimens I had packed from my own collection to loan to the teacher who was doing geology with his class (the next day, the remains of a cyclone hit and the schools were closed and the school holidays started the next day so he missed out).

As always, the kit contains bauxite samples and other stuff from our local alumina refinery. Standard stuff. But with the samples from the alumina plant was a container of what appeared to be synthetic, colourless corundum. They were crystals, some of which were transparent and clean enough to be faceted. They obviously had a high RI and were very brightly reflective and showed the hexagonal crystal growth pattern.

I didn't realize there was a technique for growing synthetic corundum that produced the proper hexagonal crystal pattern seen in natural sapphire. Then again, this stuff is from an alumina refinery so I assume the crystals are a by-product of some sort.

The container is sealed and there is no one else there to ask permission at the moment to open it up and more closely examine the material but it sure gives the visual impression of corundum to me.

Does anyone know if corundum crystals are produced in the alumina refining process?


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Wed Apr 12, 2017 11:27 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2513
Location: North Carolina
The hydrothermal growth method does produce nice hexagonal crystals, so that would be a likely candidate.


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Thu Apr 13, 2017 1:48 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1092
Location: Central Queensland, Australia
Stephen Challener wrote:
The hydrothermal growth method does produce nice hexagonal crystals, so that would be a likely candidate.


I'd only ever heard of flame-fusion being used to produce synthetic sapphire. Is it more difficult to determine that a hydrothermally grown crystal is synthetic, given that it possesses the proper crystal shape?


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Thu Apr 13, 2017 1:47 pm 
Offline
Valued Contributor

Joined: Thu Mar 19, 2015 9:55 am
Posts: 353
I haven't heard of hydrothermal sapphire being widely produced, but given the amount of synthetic, clear sapphire used to produce scratch resistant watch glasses, there must be a lot about and I don't think that flame fusion would do the trick. Anyone else any further information?


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Thu Apr 13, 2017 2:46 pm 
Offline
Gemology Online Veteran

Joined: Wed Jan 23, 2013 5:29 pm
Posts: 761
Location: Paris
I think corundum used for watch glasses is of the flame fusion type.

Flux grown and hydrothermal are 2 other types of synthetic corundums, and yes they are harder to identify, at least when cut.

But flame fusion corundum is infinitely more widespread (because easier, faster and less expensive to make).

Hydothermal corundum is the rarest of all. It is the most expensive to produce, and given the abundancy of natural corundum, it is not really worth it.

I have seen roughs of flux grown corundums, they are hexagonal too, still they don't look like their natural counterpart. Never seen hydrothermal rough for corundums, only for emeralds.


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Thu Apr 13, 2017 10:00 pm 
Offline
Gold Member
User avatar

Joined: Thu Jan 24, 2008 4:01 pm
Posts: 1738
Location: Pine City, NY and Dothan, AL
Morion has corundum produced by several methods: http://www.morioncompany.com/Products_1.htm


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Fri Apr 14, 2017 2:57 am 
Offline
Valued Contributor
User avatar

Joined: Wed Mar 26, 2014 8:23 am
Posts: 232
Location: Germany
Lefty wrote:
Does anyone know if corundum crystals are produced in the alumina refining process?

Rubis RSA France (Dalloz group) is producing his own alumina powder by calcining ammonium alun at 1200°C; which is then screened to become a Verneuil feed powder. http://www.rubisrsa.com/index.adml?r=118

More details by The Aluminum Association http://www.aluminum.org/industries/prod ... a-refining


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Fri Apr 14, 2017 4:38 am 
Offline
Gemology Online Veteran

Joined: Wed Jan 23, 2013 5:29 pm
Posts: 761
Location: Paris
I once visited the Dalloz plant. It was quite fascinating to see the "boules" in their growing process. All sizes of them.


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Fri Apr 14, 2017 5:15 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1092
Location: Central Queensland, Australia
Interesting links there, thanks.

I might ask if I can take a piece and see if it can be faceted, just for the hell of it :)


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Mon Apr 17, 2017 6:26 pm 
Offline
Gold Member

Joined: Sun Jun 28, 2009 9:56 am
Posts: 1195
Both flux and hydrothermal processes will yield crystals (with facets).


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Mon Apr 17, 2017 10:08 pm 
Offline
Gemology Online Veteran

Joined: Mon Feb 11, 2008 11:11 pm
Posts: 504
Location: Moncton, Canada
Two Ramaura flux grown ruby crystals; hexagonal growth lines are visible on the larger one.

Cheers,
Hans Durstling
Moncton, Canada

Attachment:
Ramaura-for-GO-3901 copy 2.jpg
Ramaura-for-GO-3901 copy 2.jpg [ 215.19 KiB | Viewed 199 times ]

_________________
Ecclesiastes 10:19


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Wed Apr 19, 2017 3:42 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1092
Location: Central Queensland, Australia
Well I opened the container of crystals and took one out. Taking a crappy old quartz crystal, I attempted to make a scratch on the unknown specimen - I pressed the point of the quartz crystal against the specimen....which promptly shattered into half a dozen pieces.

I picked up one of the bits and squeezed it hard between my finger and thumb and succeeded in crushing it further. I am now convinced that while the specimen may indeed be crystalline alumina, it's not in the form that we would call corundum :)

I'll bet this is what alumina looks like after extraction from the bauxite - colourless hexagonal crystals. I was going to facet a piece and put it back in the display but since it's looks like it would probably be almost as challenging as halite I don't think I'll bother.


Top
 Profile  
Reply with quote  
 Post subject: Re: Ways to make synthetic corundum?
PostPosted: Sat Apr 22, 2017 4:58 pm 
Offline
Platinum Member
User avatar

Joined: Fri Jun 25, 2010 10:06 pm
Posts: 2175
Location: Rochester, MN / Toronto, ON
Lefty wrote:
I'd only ever heard of flame-fusion being used to produce synthetic sapphire. Is it more difficult to determine that a hydrothermally grown crystal is synthetic, given that it possesses the proper crystal shape?

Corundum can actually be grown by pretty much every method. Flame fusion is the cheapest, pulled methods (like Czochralski and Kyropoulos) are used for scientific instruments and things like iPhones, flux-grown (like Chatham rubies) gives crystal habits and more "proper" pleochroism, and hydrothermal (like RusGem blue sapphires) gives the closest to natural. Floating-zone...exists and is possible but isn't really done outside of weird research, and I haven't seen anything in the literature about growing it via skull melt.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 13 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock