Time to catch up on reading, lapidary projects and binge watching TV. Stay home. Stay well.
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sun May 31, 2020 10:08 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 20 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Prasiolite from sri kanka
PostPosted: Fri Mar 20, 2020 8:51 am 
Offline
Established Member

Joined: Sun Oct 26, 2014 3:20 am
Posts: 48
Hi Good day to you,

I recently brought a 68 CT yellowish green rough stone (Sri Lankan stone). Which turned into two gem grade stones (16.67 CT and 9 CT) when I tested it, it turned out to be a Quartz (Prasiolite),

I would highly appreciate if anyone could share their knowledge regarding gemstone. I tried searching online and didn't find much information on it.
Below is the video of the stone.
https://youtu.be/3oWmnUm6QiU
Thank you in advance.

_________________
Fareen Gems
https://www.etsy.com/shop/fareengems


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Fri Mar 20, 2020 9:15 am 
Offline
Gemology Online Veteran

Joined: Thu May 12, 2016 2:18 am
Posts: 761
The video looks more like "Lemon Quartz" than Prasiolite. This is also more consistent with the Sri Lanka origin. Prasiolite is normally sourced in South America.


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Fri Mar 20, 2020 11:02 pm 
Offline
Established Member

Joined: Sun Oct 26, 2014 3:20 am
Posts: 48
1bwana1 wrote:
The video looks more like "Lemon Quartz" than Prasiolite. This is also more consistent with the Sri Lanka origin. Prasiolite is normally sourced in South America.


I seen few stone online that are similar to my stones color offered as prasiolite, Is there anyway that i could conclusively identify it. is there any special gemological property that prasiolite has ?


Thank you

_________________
Fareen Gems
https://www.etsy.com/shop/fareengems


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sat Mar 21, 2020 8:36 am 
Offline
Gemology Online Veteran

Joined: Thu May 12, 2016 2:18 am
Posts: 761
No, both are quartz. The distinction is based purely on color. No significant price difference either. Both are very inexpensive.


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sat Mar 21, 2020 9:30 am 
Offline
Established Member

Joined: Sun Oct 26, 2014 3:20 am
Posts: 48
1bwana1 wrote:
No, both are quartz. The distinction is based purely on color. No significant price difference either. Both are very inexpensive.


Thank You for you reply

_________________
Fareen Gems
https://www.etsy.com/shop/fareengems


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sat Mar 21, 2020 12:43 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 20169
Location: San Francisco
A little more information I was able to dig up from 2012:
viewtopic.php?f=11&t=15937


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sat Mar 21, 2020 6:46 pm 
Offline
Valued Contributor

Joined: Fri Jun 25, 2010 12:04 am
Posts: 171
Location: Idaho
The original (?, 1970's) praisiolite or "greened amethyst" that I remember was a medium asparagus (grayish/brownish) green, created by heating amethyst from a specific Brazilian mine. It was not called green amethyst at that time. Kind of the difference between a verb and an adjective.

The more recent stuff is a much paler color, and is reportedly irradiated and heated to get the color. Frequently hucksters falsely call it "green amethyst". https://www.neweragems.com/product-page/green-amethyst-125-00-cts

There is also a yellow-green quartz (radiation and heat) that may be called Oro Verde Quartz, Lemon Quartz, or Lime Quartz. May go from greenish to yellow in different light. https://tmsgems.com/shop/facet-rough/oroverde-qv101/

_________________
Lapidarist by Passion
Goldsmith by Necessity

Facetron x2
GemCad/GemRay/Gem Cut Studio
Matrix 9/Rhino 5, 6, 7WIP
REVO A (still hanging on...)
EnvisionTEC Micro (DIE, beast!!!)
Indutherm MC-15


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 3:06 am 
Offline
Established Member

Joined: Sun Oct 26, 2014 3:20 am
Posts: 48
Thnaks Barbra, for the great info!!

_________________
Fareen Gems
https://www.etsy.com/shop/fareengems


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 3:10 am 
Offline
Established Member

Joined: Sun Oct 26, 2014 3:20 am
Posts: 48
abeck wrote:

There is also a yellow-green quartz (radiation and heat) that may be called Oro Verde Quartz, Lemon Quartz, or Lime Quartz. May go from greenish to yellow in different light.


So most Lemon Quartz are Irradiated and heated ? is untreated Lemon Quartz rare ?

_________________
Fareen Gems
https://www.etsy.com/shop/fareengems


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 1:35 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 20169
Location: San Francisco
I have never seen naturally occurring lemon quartz. Anyone?


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 2:12 pm 
Offline
Gemology Online Veteran
User avatar

Joined: Sat May 22, 2010 2:51 am
Posts: 707
Location: Cape Town, South Africa
This summary I wrote some years ago for our local gem & mineral club may be useful here.

The Colours of Quartz

Duncan Miller

The Journal of Gemmology (2012, Vol. 33, Nos 1/4) has an excellent article by Ulrich Henn and Rainer Schultz-Güttler called ‘Review of some current coloured quartz varieties’. For those who don’t have access to this journal, published by the Gemmological Association of Great Britain, this is a short summary to help you distinguish the different varieties.

We all know that quartz occurs naturally in various colours with varietal names – colourless rock crystal, yellow citrine, purple amethyst, pink rose quartz, brown smoky quartz, black morion, and the rare natural green prasiolite. Some of these colours can be produced artificially by radiation, sometimes coupled with heating. Artificial heating can also lighten some dark coloured quartz. Given the variations in natural quartz and their different reactions to irradiation and heating, a correspondingly wide range of artificial colours can be produced.

Most colourless natural quartz contains chemical impurities, even if these do not produce visible colour. They are mainly iron, in Fe-bearing quartz, and aluminium, in Al-bearing quartz. Natural or artificial irradiation with subsequent heating causes different colours in these two different quartz varieties.

First let’s consider Fe-bearing quartz. Naturally occurring clear Fe-bearing quartz crystals can experience low-level gamma irradiation from radioactive minerals in the surrounding rock. Over long periods of geological time this produces a change in the bonding of the iron impurity atoms, which results in the violet or purple colour of amethyst. Heating most amethyst to about 450°C causes it to bleach to colourless or pale yellow. Continued heating causes precipitation of iron oxide particles, which causes a deeper yellow. Most citrine on the gemstone market is such heat-treated amethyst. Because the colour is caused by uniformly dispersed iron oxide particles, this citrine is not pleochroic, that is, it does not show different intensities of colour when viewed in different crystallographic directions. Heat treated amethyst usually shows evidence of Brazil law twinning, often with colour zoning.

Some amethyst, when heated, turns green. Natural prasiolite is very rare and probably results from natural heating of amethyst. Most prasiolite on the gemstone market is artificially heated amethyst. This colour is produced by another change in the bonding of the impurity iron atoms, rather than by the precipitation of iron oxides. This material comes from only a few sources, mainly the Montezuma mine in Minas Gerais, Brazil.

Prasiolite itself can be subjected to artificial gamma irradiation and subsequent heat treatment to produce so-called ‘blueberry quartz’. This is a deep violet blue and resembles tanzanite.

Heating amethyst above 500°C not only bleaches it but can produce a milkiness, resulting in so-called ‘neon quartz’. This looks like lilac-coloured rose quartz. Stronger heating bleaches out the lilac colour completely and tiny water droplets form in the quartz. This material resembles adularescent gem materials and may be used as imitation moonstone.

Natural ametrine is bicolour quartz, purple and yellow, mainly from the Anahí mine in Bolivia. The colouring process is complicated. It involves differing concentrations of water in different growth sectors of the crystal and natural irradiation acting on the water to inhibit the formation of the purple colour in those sectors. Artificial heat treatment of ametrine to bleach the amethyst sectors can produce bicoloured citrine/colourless stones, sometimes marketed as ‘Lunasol’.

So much for Fe-bearing quartz. What about Al-bearing quartz? Usually the concentrations of aluminium in quartz are much higher than iron. Low levels of natural irradiation of Al-bearing quartz produces natural coloured citrine – yellow, yellow-green to yellow-orange. The details of the production of colour with irradiation in Al-bearing quartz is not well understood, but with increased levels of gamma irradiation the colour darkens, producing smoky quartz, and eventually black morion. Obviously, these colours also can be produced artificially with gamma irradiation, as is the case with the black Arkansas quartz.

Al-bearing quartz can also contain lithium in significant quantities. If is it lithium-poor, morion can be bleached by heat treatment to produce smoky quartz (and presumably some yellowish smoky quartz could be bleached to citrine). If Al-bearing morion, either naturally or artificially produced, is also lithium-rich, then gentle heat treatment at below 280°C can produce yellowish-green ‘lemon quartz’.

The distinctive characteristics of untreated and treated Al-bearing quartz are that if it is coloured it is pleochroic, and that it does not show evidence of Brazil law twinning. So naturally coloured citrine will show pleochroism from pale to intense yellow and no Brazil law twinning, while citrine produced by heat treatment of Fe-bearing amethyst will show no pleochroism but Brazil law twinning may be present. Lemon quartz produced by heat treatment of Al-bearing smoky quartz will show yellow to yellow-green pleochroism but no Brazil law twinning.

Other quartz varieties exist too. ‘Greened amethyst’ is produced by artificial gamma irradiation of pale amethyst containing a very high content of water, from southern Brazil. The resulting crystals can be a deep green, with a ‘greasy’ lustre. This green quartz shows red under the Chelsea Colour Filter, while Fe-bearing prasiolite shows green. Heating above 500°C produces a cloudy opalescence due to exsolved water in very fine droplets.

Common pink rose quartz, generally described as ‘massive’ although it is crystalline, is thought to owe its pink colour to tiny included crystals of pink dumortierite. The cloudy appearance is due to scattering of light from these tiny inclusions. (In some material these inclusions must be crystallographically orientated, because they can produce asterism.) The much less common rosettes of pink quartz, usually on a white quartz crystal matrix, are essentially different from massive rose quartz. These clusters of pink single crystals have colour attributed to aluminium and phosphorus. Gamma irradiation can intensify the colour of these rosettes of single crystals to a stronger purplish pink.

The tendency of coloured quartz varieties to change colour on heating means that jewellers need to take care to avoid heating stones when repairing jewellery set with any coloured variety of quartz.


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 3:27 pm 
Offline
Gemology Online Veteran

Joined: Thu May 12, 2016 2:18 am
Posts: 761
Be aware that it is possible (and is being done in small quantities) to grow synthetic quartz in all colors that shows Brazil Law Twinning. It is not common, so many rely on this, but it is not definitive any more.


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 8:25 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 20169
Location: San Francisco
Absolutely.
But, it is my understanding that it was originally a Japanese product produced for academic purposes.
On the same subject, not all natural amethyst exhibits polysynthetic (repeatedly twinned on the Brazil law) twinning.

What to do?
GemmoFtir™?


Attachments:
Screen Shot 2020-03-22 at 5.21.05 PM.png
Screen Shot 2020-03-22 at 5.21.05 PM.png [ 220.04 KiB | Viewed 191 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 8:33 pm 
Offline
Gemology Online Veteran

Joined: Thu May 12, 2016 2:18 am
Posts: 761
Separation is possible, just not practical considering the values involved.


Top
 Profile  
Reply with quote  
 Post subject: Re: Prasiolite from sri kanka
PostPosted: Sun Mar 22, 2020 8:42 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 20169
Location: San Francisco
Again....absolutely!


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 20 posts ]  Go to page 1, 2  Next

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