Blue Garnet Color Change Green Blue, South Madagascar origin VERY RARE!

Hi Gem community!

Here is a Blue colour change Garnet, changes colour to Green Blue, to pinkish purple under incandescent light
( the blue is coloured by vanadium) , origin Bekily Madagascar.

This, I understand, may be one of the largest and rarest Blue Garnets with Green blue colour change recorded to date.


Name: Color change Garnet
Color: Blue
Weight: 16.71 carats
Cut: Mixed Oval
Measurements: 13.43 x12.20 x10.10 mm
Clarity. VVS1
Notes: No treatment, natural transparency
Colour change: Greenish blue/pinkish purple
Origin: Bekliy, Madagascar
Certification: IGI December 5th 2023, IDL March 30th 2022

The owner, who is Madagascan purchased the stone rough in 2016, when two small pockets formations were discovered in Bekily South of Madagascar. These pockets are now bare, further highlighting the rarity of the stone.

It was then cut in 2022 and certified in 2022 and 2023.

I would like understand a few things.

How can this stone be accurately valued?
The values seem to range from 100k usd per carat to 1.5m USD (Sold in 2003 for 6.8m), but what is rare doesn’t necessarily means it’s desirable or has demand.

Anyone have idea of the potential value of this Blue Garent colour change to Green blue at 16.71 carat from the pictures?

Would a specialist auction house be the correct route to facilitate a purchase sale for this stone?

What other routes should be explored to sell the stone?

See pictures:

Many Thanks in advance for your support and advise!


1 Like

What size was the garnet that sold for 6.8 million in 2003?

Hi Gary,

That one was a 4.2 carat.

Unfortunately, i don’t think its a case of just bench marking against the one in 2003.

Although considered “rare” and valuable due to its limited availability and color change, the price seems fluctuate based on supply, demand, market trends and overall desirability.

If anyone can shed some light on its current potential value (give or take) or point me in the direction of the correct experts, it would be very helpful?

The current data ranges from 2k, 7k, 80/100k all the way up to 1m usd per carat!

Real market value, maybe $2,000/ct, if you get lucky and find a willing buyer. I am a wholesale dealer with an office in Bangkok since 1990, and your estimate of “100k usd per carat to 1.5m USD” is shockingly inaccurate. Here is an example under $2,000/ct for a price comparison.

That is a chunky stone!

Some questions about it,

  1. Do the IGI and/or IDL certificates provide the standard measurements in their assessment? (RI, SG, Optical behaviors). An informed buyer will want to see these certificates especially if the asking price reaches the $2,000/ct. At least I would.

  2. Are these local Laboratories in Madagascar or are they somewhere else? I am not familiar with either one.

I understand the need to retain stone weight, the bulging pavilion is a typical method for weight retention. Its known to help sustain color hue/saturation, but at risk of darkening and/or reducing the brilliance. The very thin girdle, though… raises a red-flag for me. Assembled stones often use the girdle as the point of lamination. Convenient for hiding a layer of color enhancement.

Would like to see images of the stone in an immersion cell or with a light source shining through the girdle plane.

On a side note, the carat weight of the stone does agree with the given dimensions.

Using the formula in How to Estimate Gem Weight in a Jewelry Setting - Gem Society, the measured stone weight falls mid-range of the estimated value against the SG range for Garnets.

Garnet SG ranges from 3.4 to 4.3.

Using the Oval Cut formula: Diameter x Diameter x Depth x SG x 0.0020 gives a weight of 11.25 to 14.23 ct using the Min/Max SG. This would be for “well portioned” stone cuts.

Using the adjustments to describe a bulging pavilion, very thin girdle, and High Shoulders, the adjusted range is 14.18 - 17.93 ct.

This calculation doesn’t prove anything specific about the stone, but I thought it would be an interesting “what-if” exercise / question to ponder… :slight_smile:

Hi Jeff,

I appreciate your response. Sorry just to clarify, I was only feeding back information through some research and from the owner

I would truly like to understand why there are such huge varied valuations for this stone? The owner has very high expectations due to what she is reading but then when I show her actual market prices similar to the one you kindly posted they tell me that they may be “fake” etc or different in someway.

Thanks h

Hi Troy,

Yes the certs provide full set of measurements and description of color change (if this what you mean regards optical behaviour)

Regards the lab, both have branches in Dubai, IGI and IDL are worldwide know. The stone was tested in Dubai on both occasions. It was also tested in Madagascar but with a smaller testing lab. IDL is an official accredited test lab for the ICA

I will take some pictures of the girdle over the weekend and post if of interest.

Hi Hyder,

Yes, I would be very interested in seeing images of the girdle if it isn’t too much trouble, thank you!

Since IDL is an accredited lab with ICA, it stands for reason they would be able to test for doublet (assembled) stones, etc. Apologize, if my earlier comments seemed abrasive on their results.

It is becoming more difficult to find trustworthy labs from the local sourced areas. I have not been able to travel to any trade hubs outside of the US since visiting Taipei in 2018.