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What are Golconda diamonds?

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Ann

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Just wondering if anyone here has more info or has ever seen one. In the wee bit of info I do have, apprently they are very white and pure diamonds from India. But are they in the market? Rare?
 

Richard Sherwood

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Very rare, as the Golconda region played out in the mid 1800's (amended) (mining began around 800BC).

Nowadays when you see a Golconda for sale, it's usually out of Christies or Sotheby's, with a documented provenance, selling for big money.

Golconda was noted for producing some of the finest "D" color diamonds, as they were type IIA diamonds which contained no nitrogen (the trace element which gives varying tints of yellow body color to the "cape" series of diamonds).

The Hope Diamond (blue) and several other important diamonds of history originated from the Golconda region as well.
 

Garry H (Cut Nut)

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I have a theory that Aussie diamonds came from the same source.

(East coast of India is where Gloconda is, and NW coast of Oz is where argyle is - they were once joined in Gondwana Land)

The trouble is that aussies seemed to always have a rough ride to this island (usually in chains). Argyle diamonds were transported roughly to the surface in a lamproite volcanoe.

We make up for it with a love of all things Amber in color
 

DiamondExpert

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Garry: "We make up for it with a love of all things Amber in color" - I assume you mean Foster''s!!??
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Richard Sherwood

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Date: 9/1/2005 1:01:17 AM
Author: Garry H (Cut Nut)

The trouble is that aussies seemed to always have a rough ride to this island (usually in chains).

It cracks me up how a whole new country grew from a band of "outcasts". It''s weird how things work out, eh?

Rich, lifting a Becks...
 

valeria101

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To make things worse.
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Now you see white and brown IIa diamonds called 'Golconda type' on auction catalogs. This may come from the simple fact that type can be identified and certified by gemological laboratories while geographical origin cannot. Whatever...

I don't think any lab identifies origin for diamonds (perhaps they'd wish after the 'blood diamonds' hype) - including the good origins such as the above mentioned. The type can be identified, so chances are this is what is labeled 'Golconda' except the case of diamond jewelry datable before diamons from other sources but have become available - which is very tall order.

This is all I know...
 

diagem

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Guebelin, is the only Labratory which has identifies Golconda''s, and is acceptable by Gem Conoiseurs. But they do not mess with "Golconda Style" or what other (unheard) marketing Idea''''s!!!

There is no such thing a Golconda style, Golconda is the DIAMOND material itself!!!
 

Ann

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AGBF - thanks for the info on the threads. Some interesting reading.
 

Nicrez

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Richard, besides Golconda stones, are Type II also indicative of HPHT? If one had a D color diamond with indicative graining determining Type II is there a test to determine HPHT besides Infra red?
 

Richard Sherwood

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Date: 9/3/2005 12:36:04 AM
Author: Nicrez

Richard, besides Golconda stones, are Type II also indicative of HPHT? If one had a D color diamond with indicative graining determining Type II is there a test to determine HPHT besides Infra red?
Infra red spectroscopy, Raman-photoluminscent spectroscopy, Cathodeluminscent spectroscopy & to a lesser extent UV/VIS/NIR (ultra-violet/visible/near infra red) spectroscopy are the methods of choice for identifying Type IIA brown diamonds which have been decolorized using HPHT (high pressure, high temperature) treatment.

That said, there are some indicators which the gemologist with traditional equipment can use in identifying suspect HPHT stones for further conclusive analysis. We'll contain this discussion to the very rare, practically nitrogen free type IIA diamond which was characteristic of many Golconda diamonds. These type IIA diamonds manifest two totally different body colors, either colorless to near colorless (usually D-F and less so G-H), or varying shades of brown (and brown-pink).

The brown coloration is created from distortion of the crystal lattice rather than trace element absorption (such as nitrogen absorbtion in the blue spectrum for type IA & IB diamonds). The HPHT process "anneals" (relieves, restructures) this distortion, with a consequent "decolorization" of the stone.

The interesting thing about the resultant body color (which can be from D to H color, but from my experience is usually in the F-G range) is that any color which can be discerned is a very faint yellow rather than very faint brown. Therefore a type IIA (or type IaB, which can also be practically nitrogen free) which has a faint residual yellow body color (instead of brown) would be suspect.

So you would first determine if you're dealing with a (relatively very rare) type IIA or type IaB diamond through transparency to shortwave ultraviolet using one of the inexpensive SW testers on the market. Marty Haske makes a high quality unit for around $800 and the SSEF lab sells a nice unit for around $650 (http://www.ssef.ch/en/news/news1.html).

Then you would look for these indicators:

1. Very faint yellow (instead of brown) residual body color (F thru H).

2. Dark graphite inclusions.

3. Traces of dark graphitization within healed feathers.

4. "Burned" faceted girdles.

5. "Frosted" feathers

6. Strong banded strain patterns visible under the microscope using crossed polaroids, or sometimes darkfield illumination.

7. Usually VS clarity or better.

Remembering that these diamonds are subjected to high pressure and high temperature is helpful when searching for clues. Because the process is risky, VS and better clarities are preferred over SI or I clarities, especially with surface reaching feathers. The HPHT treatment could shatter SI-I stones, and indeed sometimes damages the VS+ as well.

The HPHT is also responsible for graphitizing inclusions, burning girdles and frosting feathers. Sometimes repolishing is required to remove "burn" characteristics from HPHT stones.

Again, these are just indicators, reasons for submitting the diamond to a major lab for further analysis. With proper equipment and trained personnel, the vast majority of HPHT stones can be conclusively identified.
 

Garry H (Cut Nut)

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Wow, that is a thorough and complete explanation Rich
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Pretty good for a gorilla
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It should be noted that type II diamonds even from gloconda would have been rare, but type II diamonds tend to be very large; because they so pure they can grow very very quickly into large free shaped crystals.

So naturally the famous stones from Glocondia that are in the historical record are the big ones.
 

Richard Sherwood

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Yeah, I find it interesting that Argyle has a significant production of Type II diamonds, which you (Garry) have pointed out in the past.

Argyle also has the distinction of being the first mine to yield blue diamonds which are not colored by absorption due to the trace element boron, but by an overabundance of hydrogen atoms.

As a consequence, they are not semi-conductors of electricity, as all the natural blues up to this point have been. A here-to-for easy screening test for a gemologist to perform to determine natural versus irradiated blue, as all irradiated blues are from non-Type II material, and are not semi-conductors.

Additionally, another interesting characteristic of these Argyle blues is that they contain a trace element which has up to this point been confined to HPHT synthetic blues.....nickel.

So no longer can a gemologist assume that a non-conducting blue diamond showing nickel spectral characteristics is irradiated, and/or an HPHT synthetic. They're going to have to look a little further.

Garry, do you know anything of the prevalence/rarity of these Argyle blues? Do they occur in large sizes?
 

diagem

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I had in my hands a 10 ct. plus Old-Mine Cut which had the orange flouresence you are talking about, it was not near the redish flo. the Hope Diamond posseses, and it didn''t last for a long time out of the flo. light.

GIA graded it a light pink shade, VS1 clarity.
Gubelin graded it a "Golconda" Fancy Pink, SI1 (due to natural chips that authenticate the antiquity of the GEM.

It was sold back in 2001 at Christies.

It was an amazing GEM!!!
 

Richard Sherwood

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Cool, DiaGem. You don''t happen to have any photos of that stone, do you?

I''m curious about the fact that the Gubelin lab gives country of origin (mine of origin) reports on (some) Golconda stones. Do you happen to know what criteria they use in determining this?

Do they do country of origin on any other diamond localities? Premier Mine cape stones seem like a likely candidate, wouldn''t you think?
 
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