Stone IDea...Leuco garnet ?

[PerSweden]

Hi all,

So glad to know about this community and its expertise. Got some 70-80 colored stones after my late father and some are not easy to identify.
Most I identified with a refractometer I also got from him and I even been able to do spot reading after lots of practice...

There are a couple of stones that I suspect could be simulants/synthetics. These where not properly kept/identified, chipped/bad cuts and "too good to be true".

The one in question could be a Grossular Leuco garnet 2.56 ct. Its very slightly pinkish. Indicating Burma. No LW florescense. But in the same bag there where a couple of deep green also grossular garnet with an excellent pinkish/red flourescense.

Refractive index gives a sharp 1.725 I scratched it with a spinell to see thats it not...Spinell 8 Grossulars 6.5-7.5

Lets talk gemstones: Ugrandites

"The rare crystalline grossular called leuco or white garnet found in Italy (Cantanzaro), Norway (Telemarken), and at Jordansmuhl, Poland is seldom faceted and used as a gemstone. No other gem mineral of its color range exhibits a singly refractive index of 1.725. Colorless crystals with a refractive index of 1.733 are found at the Jeffrey Mine near Asbestos, Quebec, Canada. A source near Georgetown, California produces material with a refractive index of 1.737 and a density of 3.506. White crystals are frequently associated with the greenish and pink material from Lake Jaco, Chihuahua, Mexico. Myanmar and China produce white garnet that is frequently carved by Chinese artists."

The photo with flourescent stone is a medium/dark green not typically mint, probably merelani grossular garnet found in the same bag. BUT this stone is inert.

Ideas and opinions highly appreciated.
Per

 

[suzanne2]

I saw the fracture and immediately thought 'glass', but after going down the wormhole of garnet identification I found that they have a conchoidal fracture, plus the RI is wrong. The other idea is garnets can be identified with a magnet.

From Wikipedia:
For gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade.

A bit more research, you can buy these little dudes at Home Depot. Have you already tried this?

Edit: There's another good community at gemology online that might be of help.

 

[Nosean]

I have several Leucogarnets in my collection. Up to 1,64 ct

A neodym magnet will not separate them. Easiest way is a refractometer ( use the pol filter). These stones have an extremely low iron content

My stones come from East Africa and show a orangepink LW fluorescence.

Bicolor combination of tsavorite and leucogarnet too - again the colorless part shows the same fluorescence.

You find my video of them on Instagram - marlowgems0711

 

[PerSweden]

Thanks for uour feedback.
There could be a very weak magnetism as,after several attempts,the stone stuck to a magnet. But could be other reasons e.g. fat...
Need a strong neodym...

I do have a refractometer (Topcon) and the 1.725 reading is sharp and cited in my post.

Not sure if what I got is a proper polaroid filter accessory to the magnifying lens but it doesnt give any different reading or colors. Excuse my ignorance but this is all new to me. But so faschinating.

Nosean, are your leucos all with a yellow tint or also pinkish? Could explain the lack of flourescense in mine.

 

[Nosean]

The pol filter is important to rule out other gems. Of course only one reading here.

Two members of the garnet group are colorless if pure - grossular and pyrope. A reading around 1,725 is a bit high for a leucogarnet variety pyrope - could be a spinel too.
But then I think a synthetic course RI natural colorless spinel should be around 1,710-1,715.

Synthetic spinel has a higher RI course Al2O3 amount is higher.

Check a corundum and a tourmaline too to see whether your refractometer works correct.

So the light pinkish near colorless could also be a pyrope. Thegemtrader offered one years ago. But I have never seen one in real life. They are extremely rare.

The magnet will not help you here but is a cheap tool and very helpful for example to separate hessonite from spessartine.

The vera rare colorless Maligarnets show no fluorescence. The eastafrican Grossular orangepink.

Wikipedia: A neodym magnet will not seperate garnet from other colorless gems - it is wrong. Very light Malaya can show a reaction course Mangan is part of spessartine and magnetic.

 

[PerSweden]

I have several Leucogarnets in my collection. Up to 1,64 ct

A neodym magnet will not separate them. Easiest way is a refractometer ( use the pol filter). These stones have an extremely low iron content

My stones come from East Africa and show a orangepink LW fluorescence.

Bicolor combination of tsavorite and leucogarnet too - again the colorless part shows the same fluorescence.

You find my video of them on Instagram - marlowgems0711

The pol filter is important to rule out other gems. Of course only one reading here.

Two members of the garnet group are colorless if pure - grossular and pyrope. A reading around 1,725 is a bit high for a leucogarnet variety pyrope - could be a spinel too.
But then I think a synthetic course RI natural colorless spinel should be around 1,710-1,715.

Synthetic spinel has a higher RI course Al2O3 amount is higher.

Check a corundum and a tourmaline too to see whether your refractometer works correct.

So the light pinkish near colorless could also be a pyrope. Thegemtrader offered one years ago. But I have never seen one in real life. They are extremely rare.

The magnet will not help you here but is a cheap tool and very helpful for example to separate hessonite from spessartine.

The vera rare colorless Maligarnets show no fluorescence. The eastafrican Grossular orangepink.

Wikipedia: A neodym magnet will not seperate garnet from other colorless gems - it is wrong. Very light Malaya can show a reaction course Mangan is part of spessartine and magnetic.

I checked RI on several corundum and tourmalines as suggested and the came out correct.

The graph from gemstonemagnetism.com suggest that Leuco could have RI below 1.73.

I got a very simple lw uv light source but expect delivery of a proper uv flashlight. Maybe the higher wattage could show some flourescense.

 

[Nosean]

It is correct for Grossular but not Pyrope which has a lower RI if colorless.

 

[PerSweden]

I have several Leucogarnets in my collection. Up to 1,64 ct

A neodym magnet will not separate them. Easiest way is a refractometer ( use the pol filter). These stones have an extremely low iron content

My stones come from East Africa and show a orangepink LW fluorescence.

Bicolor combination of tsavorite and leucogarnet too - again the colorless part shows the same fluorescence.

You find my video of them on Instagram - marlowgems0711

It is correct for Grossular but not Pyrope which has a lower RI if colorless.

So would you say its likely that my stone is a Leuco?

The gem was in a bag together with a couple of green stones, possibly grossular garnet. So it makes sense they got the same source.

 

[Nosean]

Maybe...

Or a synthetic spinel...

 

[PerSweden]

Maybe...

Or a synthetic spinel...

I will consider it as a synthetic spinell until I get any more conclusive data.

Thanks for your input.

 

[Nosean]

There are 3 possibilities for a Leuco Garnet:

The colorless core of a Mali Garnet ( Andradit-Grossular Mix) - to my knowledge no fluorescence and maybe quite pure Grossular.

The colorless to near colorless Grossular from Eastafrica and Canada - orangepink LW fluorescence.

Near colorless pyrope - only once seen and no experience about RI and LW reaction.

 

[Nosean]

We use a Raman so it would be an easy answer....

 

[PerSweden]

We use a Raman so it would be an easy answer....

So a spectrometer would easily tell if they are synthetic spinells. Can it also rule out synthetic Leuco?

Got a proper lw uv light now and the near colorless stone doesnt show any florescense.

 

[Nosean]

There is no synthetic Leuco Garnet except some experimental small stones.

Raman says it is spinel not whether natural or synthetic.

 

[PerSweden]

Ok, understand thanks.
I guess the risk of being synthetic spinell is too high to justify the cost for a Raman spectroscopy.

 

[PerSweden]

Guess these uv light photos is an extremly strong indicator those stones are indeed synthetic spinells.

A green grossularite none to weak red in lw uv light. While a synthetic spinell is violetish strong red just as I got on the photo.

 

[JackTrick]

There is no synthetic Leuco Garnet except some experimental small stones.

Raman says it is spinel not whether natural or synthetic.

My understanding is that spinel is the one stone that Raman can identify as natural or synthetic (because the two types have actually different compositions.)

Context, I recently visited a gemologist who used a Raman spectroscope to verify that two spinels I had are synthetic.

 

[JackTrick]

And a screenshot of the relevant Raman analysis!

 

[Nosean]

My understanding is that spinel is the one stone that Raman can identify as natural or synthetic (because the two types have actually different compositions.)

Context, I recently visited a gemologist who used a Raman spectroscope to verify that two spinels I had are synthetic.

Interesting...

Synthetic spinel (Verneuil) has a higher Al2O3 amount and not the 1:1 ratio MgO:Al2O3...and most in rhe market is Verneuil.

We will check if possible some synthetic spinel....

Synthetic course a near colorless natural spinel is around 1,710 and not quite high like 1,725...

 

[UluGem]

Hi everybody and thank you Nosean for a comment of yours that made me so happy, ‘Bicolor combination of tsavorite and leucogarnet too’.

I am from East Africa and I have some bicolor garnets , white and green, and I even tried to separate them but when I noticed that the green part was integrert in the white I give up because I was afraid to destroy that beauty.

When I checked the specific gravity of the whole stones they gave me 3.1 and I put them apart when my hope about having tsavorites was dead.

Thank you very much.

I will attach some pictures.

 

[UluGem]

PerSweden, thanks to you too.
Tusen takk !