Two (potentially uninformed) questions regarding tanzanite.

[Kim Bruun]

What is the dispersion of tanzanite? Some sources lists it as 20, and some sources lists it as 30. My two tanzanites definitely show a lot more fire than my pink sapphire.

Also, is the blue through violet colour range of tanzanite strictly a function of pleochroism and cutting orientation? Both my tanzanites are cut with the violet side facing up, so to speak, and the blue visible from the side. Are some tanzanites more predominately blue than violet? I have had many tanzanites in hand, but I have still to see an ultrmarine blue one in person.

And for the record, I am ashamed of my ignorance in this field, as I have stated in the past that I would be able to distinguish a tanzanite from an iolite in hand.

 

[morecarats]

The dispersion rating for tanzanite is 0.030. That''s quite a high rating -- not as high as zircon (0.039), sphene (0.051) or demantoid garnet (0.057), but higher than spinel (0.020) and corundum (0.01.

Note that the observed dispersion for a gemstone is a function not only of the dispersion rating for the material, but also the color. Lighter tones tend to display more dispersion.

Yes, some tanzanites are more blue than violet. The pleochroism of tanzanite tends to be considerably reduced by heat treatment.

 

[Kim Bruun]

Thanks! I think the dispersion is an under-appreciated aspect of tanzanite. Of my two stones, especially the lighter one (which is by no means pale) shows hot rainbow flashes (red, purple and blue seeming particularly evident).

0.030 also puts it above most garnets, and come on, what other gems combine that rich bluish violet colour with that kind of fire?

 

[T L]

I would love tanzanite, but it''s so dang brittle and soft, that kills it for me. I have one that I hardly ever wear, and with a loupe, I can still see micro-pitting. It seems like it''s difficult to have everything in one stone, high RI, great color, size, durability, but to me, durability is of paramount importance.

 

[Kim Bruun]

Sphene is even less durable, and it remains an immensely popular stone. Demantoid and benitoite are also much sought after despite being soft. Is your tanzanite set it in a ring?

My two tazanites aren''t set - they live in a box and are occasionally taken out to be admired. My mother''s tanzanite ring still looks nice, though - but she doesn''t party as hard as I do.

 

[Barrett]

One thing about tanzy is the color is also a function of lighting..all the heated blue crystals and rough I have when placed under incadescent light all show a very very good violet color...when taken outside in the sun or under flourescent light all are blue with minimal to any violet regardless of orientation of axis..I actually showed a small pic demo on ISG showing this and how greatly different types of lighting resulted in a different color..some of my unheated tanzy''s when i would get them were a violet color but never strongly saturated in violet so when I had them heated they would flip to blue but not a strong blue of course since the violet was light to begin with. Similar to the top left and bottom right two color on the violet wiki color block

 

[Barrett]

These are old pics from over a year ago..heated tanzy crystal..first one incadescent along the a/b

 

[Barrett]

Same stone same position under flour. this same color will be produced under sunlight also..i don''t have a sun pic but it''s roughly the exact same

 

[Kim Bruun]

Gorgeous crystal, sublime colours! My mom got her first tanzanite in when I was in my early teens, and since then, it has been my favourite stone.

 

[T L]

Date: 2/27/2010 9:17:39 AM
Author: Kim Bruun
Sphene is even less durable, and it remains an immensely popular stone. Demantoid and benitoite are also much sought after despite being soft. Is your tanzanite set it in a ring?

My two tazanites aren''t set - they live in a box and are occasionally taken out to be admired. My mother''s tanzanite ring still looks nice, though - but she doesn''t party as hard as I do.

Hi Kim,
Yes, but it seems to me that tanzanite is not just soft, but extremely brittle too. For example, pearl is a very soft stone, but it''s very durable.

 

[Kim Bruun]

Date: 2/27/2010 9:27:45 AM
Author: tourmaline_lover

Hi Kim,
Yes, but it seems to me that tanzanite is not just soft, but extremely brittle too. For example, pearl is a very soft stone, but it''s very durable.

I know that pearls have great tenacity and that tanzanites are brittle. It would be nice if there was a scientific scale for brittleness like there was for hardness. Still, if one can protect one''s tanzanite from knocks, is the brittleness that much of an issue? Also, are unheated tanzanites as brittle as the heated ones?

 

[LD]

This is a very interesting thread. The odd thing is that I don't look at any of my Tanzanites and think "dispersion"! I look at them and think "mmmmm love the pleochroism"! Moving the stone creates red, pink, purple, blue flashes depending on the gem but to me, it has a very different "look" than, say, a Sphene where the fire radiates out of the stone with an amazing amount of different colours.

I believe that the Tanzanites more to the blue end of the spectrum are more sought after than the violet ones and of course the lighter in colour the less the value (and conversely if too dark). For me, I love the Tanzanites that look like a royal velvet but with clarity if that makes sense?

Kim - can you post a colour of what you consider to be ultramarine because colour is so subjective? For me, ultramarine is a very bright blue and not necessarily a colour I'd want in a Tanzante but I could well be misinterpreting the colour you mean.

Amguy that crystal is beautiful. Has it been faceted?

 

[PrecisionGem]

The dispersion seen on a stone is also a function of how it is cut. There are cuts that can bring out the dispersion a lot more than others. One thing that really helps with dispersion is higher angles on the crown. Unfortunately due to the shapes of the typical tanzanite crystal, the crowns are often faceted very flat, which will kill dispersion.

 

[T L]

Date: 2/27/2010 9:35:13 AM
Author: Kim Bruun

Date: 2/27/2010 9:27:45 AM
Author: tourmaline_lover

Hi Kim,
Yes, but it seems to me that tanzanite is not just soft, but extremely brittle too. For example, pearl is a very soft stone, but it's very durable.

I know that pearls have great tenacity and that tanzanites are brittle. It would be nice if there was a scientific scale for brittleness like there was for hardness. Still, if one can protect one's tanzanite from knocks, is the brittleness that much of an issue? Also, are unheated tanzanites as brittle as the heated ones?

I don't know if heating affects the brittleness of tanzanite, but even wiping it down causes scratching and micropits. It's a pity really. I have some sphene I keep in boxes too. I know LD would disagree with me about setting them, but I'm just always worried about them. For this reason, I love spinel. I have a couple that look like tanzanite, and I wouldn't be afraid to wear them on a daily basis. In fact, I have one set now that I wear almost every day. I love it, and it looks just like a tanzanite. It has sparks of blue and pink coming off of it as well. My jeweler was dumbfounded that it was a spinel and not a tanzanite.

 

[LD]

Date: 2/27/2010 9:48:22 AM
Author: tourmaline_lover

Date: 2/27/2010 9:35:13 AM
Author: Kim Bruun

Date: 2/27/2010 9:27:45 AM
Author: tourmaline_lover

Hi Kim,
Yes, but it seems to me that tanzanite is not just soft, but extremely brittle too. For example, pearl is a very soft stone, but it''s very durable.

I know that pearls have great tenacity and that tanzanites are brittle. It would be nice if there was a scientific scale for brittleness like there was for hardness. Still, if one can protect one''s tanzanite from knocks, is the brittleness that much of an issue? Also, are unheated tanzanites as brittle as the heated ones?

I don''t know if heating affects the brittleness of tanzanite, but even wiping it down causes scratching and micropits. It''s a pity really. I have some sphene I keep in boxes too. I know LD would disagree with me about setting them, but I''m just always worried about them. For this reason, I love spinel. I have a couple that look like tanzanite, and I wouldn''t be afraid to wear them on a daily basis. In fact, I have one set now that I wear almost every day. I love it, and it looks just like a tanzanite. It has sparks of blue and pink coming off of it as well. My jeweler was dumbfounded that it was a spinel and not a tanzanite.

Goodness me! What are you using? Wire wool?

Honestly that SHOULDN''T happen at all. Are you 100% positive that what you''ve got is a Tanzanite?

 

[LD]

This is NOT a high quality Tanzanite by any stretch of the imagination but it''s an unusual cut and it shows the pleochroism well. Is this what you''re seeing Kim?

 

[MakingTheGrade]

I love that cut LD. My tanz in my avatar is mostly blue outdoors and more violet inside. But always Flashing lovely colors.

I know they''re brittle so I put it in a pendant. But wish I had a ring instead so I could admire it more easily.

 

[T L]

Date: 2/27/2010 9:54:52 AM
Author: LovingDiamonds

Date: 2/27/2010 9:48:22 AM
Author: tourmaline_lover

Date: 2/27/2010 9:35:13 AM
Author: Kim Bruun

Date: 2/27/2010 9:27:45 AM
Author: tourmaline_lover

Hi Kim,
Yes, but it seems to me that tanzanite is not just soft, but extremely brittle too. For example, pearl is a very soft stone, but it's very durable.

I know that pearls have great tenacity and that tanzanites are brittle. It would be nice if there was a scientific scale for brittleness like there was for hardness. Still, if one can protect one's tanzanite from knocks, is the brittleness that much of an issue? Also, are unheated tanzanites as brittle as the heated ones?

I don't know if heating affects the brittleness of tanzanite, but even wiping it down causes scratching and micropits. It's a pity really. I have some sphene I keep in boxes too. I know LD would disagree with me about setting them, but I'm just always worried about them. For this reason, I love spinel. I have a couple that look like tanzanite, and I wouldn't be afraid to wear them on a daily basis. In fact, I have one set now that I wear almost every day. I love it, and it looks just like a tanzanite. It has sparks of blue and pink coming off of it as well. My jeweler was dumbfounded that it was a spinel and not a tanzanite.

Goodness me! What are you using? Wire wool?

Honestly that SHOULDN'T happen at all. Are you 100% positive that what you've got is a Tanzanite?

Yes, it's a tanzanite, and I've read about this micropitting before in an gemological article numerous years ago, so when I louped my stone, I wasn't surprised to see the micropits. I bought the stone before anyone even knew what tanzanite was, even the jewelry channels. Facet abrasion is common with tanzanite too from what I hear if you wear it often.

ETA: Here's an article on the brittle nature of tanzanite, and in one of the up close pictures you can see some micro-chips (or pits as I like to call them). They tend to be along the facet edges.

http://www.ganoksin.com/borisat/nenam/working_with_tanzanite.htm

 

[Kim Bruun]

I CAN tell plechroism from dispersion - I''m not a complete simpleton.

In my lavender stone, there are small, rainbow-like flashes when the light strikes it just right - the red is striking, but it shifts into yellow, green, and blue as well. The effect is not as pronounced as in my sphene, but it is definitely there.

 

[T L]

Date: 2/27/2010 10:10:17 AM
Author: Kim Bruun
I CAN tell plechroism from dispersion - I''m not a complete simpleton.

In my lavender stone, there are small, rainbow-like flashes when the light strikes it just right - the red is striking, but it shifts into yellow, green, and blue as well. The effect is not as pronounced as in my sphene, but it is definitely there.

Perhaps you can only see this dispersion in lighter stones. For example, it''s more difficult to see the dispersion in darker green demantoids.

 

[Kim Bruun]

Geez, you guys are sceptical! It's not like I've seen a UFO or had the Virgin Mary appear to me. I'm just saying that in my trillion cut lavender tanzanite, I see the same effect that I see in my sphene, albeit to a lesser extent.

And tourmaline_lover, if tanzanite developes micropitting as a result of being wiped, wouldn't the same be true of other stones in the hardness range of 6 - 7? (And let's not even begin to consider sphene!) I would think that any damage done to the stone's surface by whiping it with a clean cotton cloth would be a result of its softness rather than its brittleness.

 

[T L]

I''m not skeptical Kim, I believe you. I''m not much of a tanzanite person, so if you say you see dispersion, I believe you. I just know that on some species of gems, dispersion is easier to see if the stone is lighter toned.

 

[Kim Bruun]

Date: 2/27/2010 10:34:46 AM
Author: tourmaline_lover
I''m not skeptical Kim, I believe you. I''m not much of a tanzanite person, so if you say you see dispersion, I believe you. I just know that on some species of gems, dispersion is easier to see if the stone is lighter toned.

Obviously. I haven''t compared my lighter tanzanite and my darker one side by side, but it is definitely my impression that the fire is more visible in the lighter stone.

 

[chrono]

I just had to jump in to comment on the lovely rough Am Guy posted showing a lovely blue and pink, and also LD''s awesomely cut pendant and setting, which while it may not be the best coloured, the cutting makes the best use of the material, showing it at its best!

 

[T L]

Date: 2/27/2010 10:49:28 AM
Author: Chrono
I just had to jump in to comment on the lovely rough Am Guy posted showing a lovely blue and pink, and also LD''s awesomely cut pendant and setting, which while it may not be the best coloured, the cutting makes the best use of the material, showing it at its best!

I agree - beautiful stones in the pendant and the crystal.

BTW, here''s a photo of a supposedly top color tanzanite I saw at the Field Museum in Chicago.

I don''t expect to see much dispersion on this stone because it was so dark, yet it was a vivid gem. My photo stinks.

 

[chrono]

I have seen a lot of medium dark toned tanzanites with saturated colour and they don''t show much dispersion although they have awesome blue/purple flashes.

 

[LD]

Date: 2/27/2010 10:10:17 AM
Author: Kim Bruun
I CAN tell plechroism from dispersion - I''m not a complete simpleton.

In my lavender stone, there are small, rainbow-like flashes when the light strikes it just right - the red is striking, but it shifts into yellow, green, and blue as well. The effect is not as pronounced as in my sphene, but it is definitely there.

I wasn''t suggesting for a moment that you were!

I have never seen yellow, green or rainbow flashes in a Tanzanite. Blue, purple, red, pink yes. After you posted I got mine out of the safe, walked around the house, looked under different lighting conditions, took them outside and couldn''t see a yellow flash at all. I''d love to see yours if you can capture it in a photo. Is your gem towards the lighter end of the spectrum i.e. a violet as opposed to purple?

I wonder if, as TL has suggested, that it depends also on the level of saturation of the stone?

 

[jstarfireb]

Here''s a more pure blue tanzanite, at least face-up:
http://www.thegemtrader.com/Feb%2010%20Tanzanite%20Page.htm

FWIW, I don''t see rainbow flashes in mine either, just the pink/purple/etc ones. But none of my tanzanites are of really great quality...they''re mostly department/mall store material.

 

[smitcompton]

Hi All,

I love the color of tanzanite. I have one that is a beautiful blue, the other a pretty medium light with a violet cast rather than blue. I want a larger tanzanite. But the so-called high quality ones seem too dark. TL''s new color change stone (ring)is beautiful. That reminds me of tanzanite.

LD, I believe you said you had an 18 ct tanzanite. Is this dark? Could you show it?

I think I do get dispersion in my blue trilliant tanzanite, but I can''t check it out now. I have heard it said that the trilliant cut is the best cut for tanzanite.

Thanks,

 

[LD]

Date: 2/27/2010 1:47:59 PM
Author: smitcompton
Hi All,

I love the color of tanzanite. I have one that is a beautiful blue, the other a pretty medium light with a violet cast rather than blue. I want a larger tanzanite. But the so-called high quality ones seem too dark. TL''s new color change stone (ring)is beautiful. That reminds me of tanzanite.

LD, I believe you said you had an 18 ct tanzanite. Is this dark? Could you show it?

I think I do get dispersion in my blue trilliant tanzanite, but I can''t check it out now. I have heard it said that the trilliant cut is the best cut for tanzanite.

Thanks,

I won''t hijack the thread but I think it''s somewhere in here:
https://www.pricescope.com/community/threads/are-you-bored-with-tanzanite-yet.129542/