How to grade a benitoite?

[liao]

I never deal with benitoite before, but I found several interesting benitoites. what do you think these benitoite:

http://www.thegemtrader.com/Feb%2009%20Ben%20Page.htm
http://www.thegemtrader.com/Nov%2007%20Benitoite%20Page.htm
http://www.thegemtrader.com/Dec12BCBenPage.htm

http://wsfgems.com/benito.html
-> .21ct Benitoite: 4.1 x 3.2mm Oval.
-> .22ct Benitoite: 4.1 x 3.1mm Oval.
-> .27ct Benitoite: 4.5 x 3.2mm Oval.
-> .33ct Benitoite: 4.2 x 3.5mm Oval.

 

[Marlow]

Benitoite has

a nice range of colors from colorless to deep blue
a fantastic dispersion
a beautiful dichroism

What you need is a color line - five to six round little stones same size - then you will see the color you love the most! I would buy this first!!

I prefer colorless ( rare ) to light or light to medium blue the see the fantastic dispersion.

Some medium blue are a bit greenish grey masked (dichroism is the reson for that) and deeper blue often have a deep pavillion course of the precious weight. Deep blue is vertical to the c-axis - so most stones are ovals or pears.

Try to get round or trillions! Emerald cuts are awesome too. Avoid sleepy stones or included stones.

WSF is a very good source, Gemtrader too, rarestone.com and Rick Kennedy ( Earthreasure) are vwry good. Avoid Capistrano - they have nice material too but they are too expensive.

 

[liao]

Benitoite has

a nice range of colors from colorless to deep blue
a fantastic dispersion
a beautiful dichroism

What you need is a color line - five to six round little stones same size - then you will see the color you love the most! I would buy this first!!

I prefer colorless ( rare ) to light or light to medium blue the see the fantastic dispersion.

Some medium blue are a bit greenish grey masked (dichroism is the reson for that) and deeper blue often have a deep pavillion course of the precious weight. Deep blue is vertical to the c-axis - so most stones are ovals or pears.

Try to get round or trillions! Emerald cuts are awesome too. Avoid sleepy stones or included stones.

WSF is a very good source, Gemtrader too, rarestone.com and Rick Kennedy ( Earthreasure) are vwry good. Avoid Capistrano - they have nice material too but they are too expensive.

do you mind giving me a short lecture about a,b,c-axis? If I remember correctly, c-axis is the 'length' axis of the rough stone right?

I have something like this
http://www.thegemtrader.com/Jan%2011%20BenSet%20Page.htm

And I prefer something similar to second one from the left. If you have a gia gemset, it is close to vB5/4

 

[Marlow]

http://www.mindat.org/min-624.html

Look at the rotating crystal. You can move it with you mouse or finger (ipad)

Rotate it in a position when see exactly the triangle - this is the view along the c-axis. The pale color. Many trilliants, rounds and "windowed " stone are cut with the table vertical to the c-axis.

Rotate it in a position when you exactly look from the side at the crystal. This is the direction with the strongest color - you see why many cut as ovals or pears.

The c-axis it not the longest - in aquamarine the crystal is often a long prism -o.k.

Morganite is often tabular shaped - the c-axis is shorter than a and b.

In Benitoite you see the orientation easy with a dichroscope.

The second left is perfect - my favorite too - but this whole set is gorgous!! The colorless and light blues will look like diamonds - this gem is the closist natural gem to blue diamond.

 

[T L]

http://www.mindat.org/min-624.html

Look at the rotating crystal. You can move it with you mouse or finger (ipad)

Rotate it in a position when see exactly the triangle - this is the view along the c-axis. The pale color. Many trilliants, rounds and "windowed " stone are cut with the table vertical to the c-axis.

Rotate it in a position when you exactly look from the side at the crystal. This is the direction with the strongest color - you see why many cut as ovals or pears.

The c-axis it not the longest - in aquamarine the crystal is often a long prism -o.k.

Morganite is often tabular shaped - the c-axis is shorter than a and b.

In Benitoite you see the orientation easy with a dichroscope.

The second left is perfect - my favorite too - but this whole set is gorgous!! The colorless and light blues will look like diamonds - this gem is the closist natural gem to blue diamond.

I like benitoite, but I think some well cut blue spinels also come very close to a blue diamond, although I don't think either really could be a blue diamond simulant. If sphalerite ever came in blue, then that would be a more natural blue diamond simulant.

 

[Marlow]

Agree,

Sphalerite with a hardness of 7-8 !!! Same with titanite....

Have you seen nice stibiotantalite??? I have a small pure yellow ( would be intense yellow in diamond) one - 0,53 ct - this material is awesome but heavy - looks like a 0,30 ct diamond! A top color for this material!!

http://www.classicgems.net/gem_stibiotantalite.htm

 

[T L]

Agree,

Sphalerite with a hardness of 7-8 !!! Same with titanite....

Have you seen nice stibiotantalite??? I have a small pure yellow ( would be intense yellow in diamond) one - 0,53 ct - this material is awesome but heavy - looks like a 0,30 ct diamond! A top color for this material!!

http://www.classicgems.net/gem_stibiotantalite.htm

The thing with sphene (titanite) is that it still doesn't have the same refractive properties of a diamond, but sphalerite comes pretty darn close. I've seen round brilliant yellow sphalerite that most novices would be hard pressed to guess were not diamond.

Do I have to say "stibiotantalite" three time fast?

It looks like Brad from thegemtrader.com had some.

 

[Marlow]

No, say "vayrynenite" three times !

 

[Marlow]

http://www.nhm.org/site/research-collections/mineral-sciences/butterfly-collection

Scroll a bit down an you see a stibiotantalite butterfly

 

[T L]

http://www.nhm.org/site/research-collections/mineral-sciences/butterfly-collection

Scroll a bit down an you see a stibiotantalite butterfly

Thanks for the link, those are some gorgeous butterflies. The benitoite one shows some nice stones, which would be of help to the OP on what colors are optimal in these gems.

I don't think I can say any of these mineral names three times fast , except beryl.

 

[chrono]

Too early for tongue twisters - let me have some coffee (maybe with a shot or two) to loosen my tongue first. In any case, the second from the left would be the ideal colour for me as well. Not too dark but not too light to allow dispersion to show.

 

[liao]

what do you think about this one?

http://www.thegemtrader.com/Jan%2010%20Benitoite%20Page.htm

 

[Marlow]

Very nice, a bit grey!

 

[liao]

Very nice, a bit grey!

that is exactly what I thought. too gray I think the color around vB3/3

should I snatch this one The cutting is not that good either

 

[Marlow]

No, go for one of the WSF stones you like....

I remember a bright light blue pear - 0,62 ct.

The best deal is the 0,96 ct - 0,05 ct more and the price pct is 3000 and not 1800!!!!!

 

[liao]

No, go for one of the WSF stones you like....

I remember a bright light blue pear - 0,62 ct.

The best deal is the 0,96 ct - 0,05 ct more and the price pct is 3000 and not 1800!!!!!

it is a great deal, but I will not put any weird triangle shaped benitoite into my collection.

Thanks. I think I will get the 0.62 or 0.73ct one

 

[Marlow]

Yes, both a really nice!! And the size is very good.

And hurry up - here are a lot of lurkers!!!

And if possible take the round 0,26 ct too - 600 pct is top! Normally aroud 900-1000 pct.

 

[Starzin]

Marlow - thank you for the link to the rare stone butterflies! A treat to see some of these rarer stones set

 

[Marlow]

And some are not really expensive and worth to try - except for a ring maybe...

 

[liao]

I just email them. Honestly, I am not sure about the 0.26ct, it is too dark. I hope these benitoite is not sold yet (like that beautiful cat's eye from TGT)

 

[Marlow]

I think his pictures are often too dark - look at the rhodolites and tanzanite.

 

[chrono]

Depends on how picky you are - if you just want something nice, then get it. If you are picky, I'd keep looking.

 

[liao]

I just received the benitoite. Honestly, I am not whether the 0.62ct is a real benitoite. The 'lower value' of the refractive index is off quite a lot. It is exactly 1.75. I have not check the density, because I left my gem scale home. Currently, I am visiting my son, and ask the stone to be shipped here

The 0.26ct, on the other hand, is undoubtedly benitoite. the refractive index match the value in mindat, but the color is pretty dark

 

[Marlow]

Yes, you only see one reading course the other is around 1,80 ! It is ok.

You will see doubling of the pavillion facet with your 15x loupe. Buy a dichroskope and you see - even in the pale blue - the strong dichroism.

The deep blue tend to be dark - thats why I prefer the pale blue variety. But price and size is very good. Take it in sunlight.

 

[liao]

yeah the 'upper' is correct. Anyway, do you know where can I find the liquid for refractometer in US, or perhaps in nyc? I am almost running out of it, and the one near my home is ridiculously expensive

what do you mean by "doubling of the pavillion facet"? And how do you know I have 15x loupe? I think most people are using 10x loupe. are you an oracle?

 

[Marlow]

You post it before that you have a 15x loupe.

The RI liquid is very expensive - esp. if you need an RI around 1,81 ( mine stops around 1,795)

I don't know in US. Google Anderson liquid, Maybe Rubin & Son ...

Need a new one too - really expensive

If you look with your through the table facet down to the facets of the pavillion you see ( like zircon or sphene) a doubling of the facets.

Depend a bit on the orientation of the stone so move it a bit ...

You like the pear?

 

[T L]

I just received the benitoite. Honestly, I am not whether the 0.62ct is a real benitoite. The 'lower value' of the refractive index is off quite a lot. It is exactly 1.75. I have not check the density, because I left my gem scale home. Currently, I am visiting my son, and ask the stone to be shipped here

The 0.26ct, on the other hand, is undoubtedly benitoite. the refractive index match the value in mindat, but the color is pretty dark

Does it fluoresce under short wave UV? If not, it's not a benitoite.

 

[Marlow]

It is!!!

Sorry, but this vendor will not sell a fake!!! To my knowledge he cuts the stones - and his father together with the Gray family run the mine for a few years!!! They still have a lot of rough...

 

[liao]

You post it before that you have a 15x loupe.

The RI liquid is very expensive - esp. if you need an RI around 1,81 ( mine stops around 1,795)

I don't know in US. Google Anderson liquid, Maybe Rubin & Son ...

Need a new one too - really expensive

If you look with your through the table facet down to the facets of the pavillion you see ( like zircon or sphene) a doubling of the facets.

Depend a bit on the orientation of the stone so move it a bit ...

You like the pear?

I know it is expensive, but this one is absurd. He asked for a freaking $400 for 10gram. Well, that pear is pretty descend, the color is okay, but the 'spark' is not that great. it looks like a plastic cut diamond rather than benitoite. I think I will give it to one of my client, since she has been longing for benitoite