Rainbow Moonstone, Cab or faceted?

[LC2016]

I have a glorious rainbow moonstone cab that I was selling a few years ago. Then I DROPPED IT while taking a video. And it freaking chipped. Still angry at myself for it. Haven't had it recut/polished because I just get furious whenever I look at it and remember that I made such a silly mistake of trying to video over hard tile floor.

I feel for you because It happened to my one other moonstone too. But thanks for reminding I immdiately put it back to the drawer after photo shooting.

 

[fredflintstone]

I have a glorious rainbow moonstone cab that I was selling a few years ago. Then I DROPPED IT while taking a video. And it freaking chipped. Still angry at myself for it. Haven't had it recut/polished because I just get furious whenever I look at it and remember that I made such a silly mistake of trying to video over hard tile floor.

I feel your pain!

In the past I cannot count the stones dropped inside my office or outdoors. Most of the times they were okay, but a few did chip, A few I could never find again dropped outside and others it took me hours to find. Very risky taking stones outside to do videos because there is always that chance, they can be dropped and chipped or lost in the grass or snow. I got to the point in the past I would not do videos outside in the winter when there was snow on the ground. Thick grass is not much better. Dropped a few on cement and unless you see where they bounce it can be a real pain to find them. One would not think a stone could bounce so far away, LOL!

 

[fredflintstone]

This thread got me thinking, what causes the colours of rainbow moonstone?

The standard story about both orthoclase moonstone and labradorite is that they have sets of thin layers with alternating composition. These, by interference, reflect light in a preferred range of wavelengths. This makes sense for orthoclase moonstone and 'blue rainbow moonstone', which show a single colour. But what causes the multiple colours? Do different parts of the stone have layers with different spacing? Or are there intersecting sets of layers?

My little cab, mentioned above, is typical in showing mostly brighter yellow-orange and fainter blue:

(Rainbow moonstone cab on black felt, lit by single flashlight, two pictures)
(Note: fredflinstone is right about photos on black. But I'm trying to understand the stone, not sell it.)

The problem with these pictures is that it's hard to make sense of what you see, because weird reflections complicate everything. To reduce the reflections, I photographed the stone in glycerine (RI 1.46 vs 1.56 for labradorite. Not a perfect match, but it's what was to hand). This showed that there are two special orientations, one reflecting orange and the other reflecting blue:

(Rainbow moonstone cab in glycerine, left showing orange, right showing blue. Note different exposure - IRL the blue much fainter than the orange - see background.)

These pictures show that the whole stone reflects orange in one orientation and blue in another - it's not that different parts reflect different colours. So it seems there are intersecting sets of layers, or maybe very fine zoning.

The fabulous example fredflintstone linked to is a bit different:

The stone has obvious zoning. It's mostly orange and blue, but there is also a yellow 'block', indicated by the white lines in the left picture. (This is clearer in the right picture and especially clear in the video.) This adds to the range of colour.

There's a fair bit of gemmological literature on labradorite, but nothing I've found that directly addresses the multiple colours of rainbow moonstone. If anyone knows of any, I'd be interested to hear.

I don't know if it was someone from here, but that Rainbow Moonstone sold right after I put a link to it.

I hope whoever bought it will be happy!

 

[Starstruck8]

Indeed I think Madagascar and India labradorite are built slightly different.

For the India one, if I tilt the stone slightly it will show a different color for each reflecting layers, but one color per layer/line (sorry for my photography, thats the best i can do on iphones)



However for Madagascar one, I actually saw multiple color for one layer, the one I have show a full spectrum of rainbow per layer on a certain viewing angle, which makes them extra colorful. And of course I do not know what cause the difference between the two type of stone.

Those pictures are fascinating! They show the magic of rainbow moonstone.

I suspect that the 'full spectrum of rainbow' colours may be the result of mixing different colours from reflections - cabs can produce very weird reflections. It might be interesting to dunk your stones, as I did, and light them with a single flashlight. This will reduce the refraction and reflections, so you can see more clearly what's caused by the material itself, as opposed to the cut.

Here is a list of RIs of common household liquids:
https://www.gemsociety.org/article/refractive-index-list-of-common-household-liquids/
You may not be able to match labradorite RI (about 1.56) exactly, but even getting close helps.

Of course, if you're not a geek like me, or don't want to dunk your stones, I quite understand...

 

[LC2016]

Those pictures are fascinating! They show the magic of rainbow moonstone.

I suspect that the 'full spectrum of rainbow' colours may be the result of mixing different colours from reflections - cabs can produce very weird reflections. It might be interesting to dunk your stones, as I did, and light them with a single flashlight. This will reduce the refraction and reflections, so you can see more clearly what's caused by the material itself, as opposed to the cut.

Here is a list of RIs of common household liquids:
https://www.gemsociety.org/article/refractive-index-list-of-common-household-liquids/
You may not be able to match labradorite RI (about 1.56) exactly, but even getting close helps.

Of course, if you're not a geek like me, or don't want to dunk your stones, I quite understand...

I just noticed most of them are oil….

 

[Starstruck8]

I just noticed most of them are oil….

Yep. Take appropriate precautions, of course. It's no worse than using oil in cooking. Clean the fluid off with detergent when finished. Then you will have a nice clean stone...

As long as the stone has no serious cracking, the fluid should not leave any permanent residue. Note that gemmological labs use similar but nastier fluids.

 

[LC2016]

Those pictures are fascinating! They show the magic of rainbow moonstone.

I suspect that the 'full spectrum of rainbow' colours may be the result of mixing different colours from reflections - cabs can produce very weird reflections. It might be interesting to dunk your stones, as I did, and light them with a single flashlight. This will reduce the refraction and reflections, so you can see more clearly what's caused by the material itself, as opposed to the cut.

Here is a list of RIs of common household liquids:
https://www.gemsociety.org/article/refractive-index-list-of-common-household-liquids/
You may not be able to match labradorite RI (about 1.56) exactly, but even getting close helps.

Of course, if you're not a geek like me, or don't want to dunk your stones, I quite understand...

I believe those should be from the material itself.

This is the other labradorite I have, (I believe its from India since I got the stone for over 10 years). The rainbow color, although quite weak comparing to the blue color, is running along the reflecting layers of the stone and goes a full circle over dome of the stone. I dont see such type of optical effect on my moonstone cab.

 

[Starstruck8]

I believe those should be from the material itself.

This is the other labradorite I have, (I believe its from India since I got the stone for over 10 years). The rainbow color, although quite weak comparing to the blue color, is running along the reflecting layers of the stone and goes a full circle over dome of the stone. I dont see such type of optical effect on my moonstone cab.

More magical pictures!

"The rainbow color [...] goes a full circle over dome of the stone. I dont see such type of optical effect on my moonstone cab." Does top stone have a higher, more curved dome and the bottom stone a lower, flatter one? Broadly, the more curved the dome, the smaller the colour patches and the less they move as the stone is tilted. The flatter the dome, the bigger the colour patches and the more they move as the stone is tilted. This applies regardless of the material. I suspect that's what's happening here.

On the colours, it's not so easy to 'read' the pictures. The surface reflections in the top picture appear to show multiple lights. In the lower picture, they appear to show two lights (the two small white rectangular/trapezoidal patches - or is one of them a reflection from the back?). This makes the pictures hard to interpret.

In the lower picture, the glow patches look overexposed. Maybe you could reduce the exposure, even if it makes everything else too dark.

I'm pretty sure that the (sorta) green I sometimes see in my stone is just a mix of orange and blue. I suspect this may apply to your stones too.

If you want to understand the stones (as opposed to just appreciating them!),
I suggest lighting the stones with a single flashlight and playing with the tilt of the stone and the position of the flashlight. This will make it easier to distinguish the surface reflection, the direct glow patch, reflections from the back and 'reflected' glow patches. But that's still tricky. If you really want to understand the stones, dunk them. This will eliminate the confusing reflections, or at least reduce them.

 

[LC2016]

More magical pictures!

"The rainbow color [...] goes a full circle over dome of the stone. I dont see such type of optical effect on my moonstone cab." Does top stone have a higher, more curved dome and the bottom stone a lower, flatter one? Broadly, the more curved the dome, the smaller the colour patches and the less they move as the stone is tilted. The flatter the dome, the bigger the colour patches and the more they move as the stone is tilted. This applies regardless of the material. I suspect that's what's happening here.

On the colours, it's not so easy to 'read' the pictures. The surface reflections in the top picture appear to show multiple lights. In the lower picture, they appear to show two lights (the two small white rectangular/trapezoidal patches - or is one of them a reflection from the back?). This makes the pictures hard to interpret.

In the lower picture, the glow patches look overexposed. Maybe you could reduce the exposure, even if it makes everything else too dark.

I'm pretty sure that the (sorta) green I sometimes see in my stone is just a mix of orange and blue. I suspect this may apply to your stones too.

If you want to understand the stones (as opposed to just appreciating them!),
I suggest lighting the stones with a single flashlight and playing with the tilt of the stone and the position of the flashlight. This will make it easier to distinguish the surface reflection, the direct glow patch, reflections from the back and 'reflected' glow patches. But that's still tricky. If you really want to understand the stones, dunk them. This will eliminate the confusing reflections, or at least reduce them.

Do you mean its actually just orange and blue and the rest of the color is possibly a mixture of the two colour?

 

[acaw2015]

Just want to say, what an interesting read. Thank you all! And... Now I have another thing on my wishlist, thanks to pricescope....

 

[Mrsz1ppy]

I don't know if it was someone from here, but that Rainbow Moonstone sold right after I put a link to it.

I hope whoever bought it will be happy!

I confess, it was me. It’s not here yet, but will post photos when I get it. Didn’t have one.

 

[Starstruck8]

Do you mean its actually just orange and blue and the rest of the color is possibly a mixture of the two colour?

For my little stone, yes, most likely. The dunking test shows that my stone only gives orange and blue schiller. These could plausibly mix to a poor green. It's also possible that you could see mixtures with the complements of the basic orange and blue (if orange or blue have been 'schillered' out the incident light, which is then reflected from the back.

The stone fredflintstone linked to and Mrsz1ppy bought is different - it appears to have parts with orange and blue schiller and parts with yellow and blue schiller.

I don't know about your stones. Just going by the pictures, they look more like mine, with only two basic schiller colours. But you can study them more closely. Dunking would be the surest way to tell...

@MrszIppy, I did wonder when I noticed that it had sold. I look forward to seeing your pictures.

 

[fredflintstone]

I confess, it was me. It’s not here yet, but will post photos when I get it. Didn’t have one.

I hope it is everything you wanted.

Please let us know!

 

[Mrsz1ppy]

I hope it is everything you wanted.

Please let us know!

Will do! Only have blues, but I love them.

 

[Mrsz1ppy]

For my little stone, yes, most likely. The dunking test shows that my stone only gives orange and blue schiller. These could plausibly mix to a poor green. It's also possible that you could see mixtures with the complements of the basic orange and blue (if orange or blue have been 'schillered' out the incident light, which is then reflected from the back.

The stone fredflintstone linked to and Mrsz1ppy bought is different - it appears to have parts with orange and blue schiller and parts with yellow and blue schiller.

I don't know about your stones. Just going by the pictures, they look more like mine, with only two basic schiller colours. But you can study them more closely. Dunking would be the surest way to tell...

@MrszIppy, I did wonder when I noticed that it had sold. I look forward to seeing your pictures.

For science!

 

[Bunnie]

I confess, it was me. It’s not here yet, but will post photos when I get it. Didn’t have one.

Did your moonstone arrive yet? Was it everything you hoped for? I’m eyeing that seller too, he’s got a lot of gorgeously gemmy moonstones

 

[LC2016]

Hey guys!!! I am needing you guys opinion, one of my vendor send me video of this stone (since I dont know how to upload a video, so Im capturing the screenshot of the video).

Its a big stone, almost 16ct quoting at 450 per ct, and quite colourful under sunlight. However the sheen is not as strong as I would like it to be.


Would you think its a good choice, or I should wait for a better one?

In fact I have seen one more stone selling by another IG vendor, 13 ct, 800 per ct (kinda crazy tbh), good sheen but super weird cut (they said its sugarloaf but its like an incomplete faceted stone to me)

 

[LC2016]

Adding another photo of the first stone i take under room light, the colorplay is weaker under room light and strength of the sheen definately cant compare with my cab

 

[Mrsz1ppy]

Did your moonstone arrive yet? Was it everything you hoped for? I’m eyeing that seller too, he’s got a lot of gorgeously gemmy moonstones

Hi @Bunnie
Sorry I have been away. Yes, the moonstone arrived. It is just as pictured by the vendor. I have been frantically gardening now that we have some clear days, so my fingers are not photo worthy. Will use my daughter’s hands when she gets up!

 

[fredflintstone]

Hi @Bunnie
Sorry I have been away. Yes, the moonstone arrived. It is just as pictured by the vendor. I have been frantically gardening now that we have some clear days, so my fingers are not photo worthy. Will use my daughter’s hands when she gets up!

Good for you. I thought it was a nice stone. Glad you like it!

 

[fredflintstone]

I'm not sure I quite understand what you are implying with both posts. The first post you said it is the vendor's still from a video. The second post which I'm replying here to, you say you took the picture. This is the same faceted Rainbow Moonstone, right?

On your first post the background is fairly white, this will under enhance the stones color play just like a white background does to Opal. While a black background over enhances the color play of Rainbow Moonstone and Opal. Also, just like Opal, different light sources produce different results with color play of Rainbow Moonstone.

 

[Mrsz1ppy]

It looks like the vendor’s pictures in artificial light. Here is late afternoon sun in the Pacific NW.

 

[Autumn in New England]

It looks like the vendor’s pictures in artificial light. Here is late afternoon sun in the Pacific NW.

Isn't that lovely! Enjoy it!!

 

[Starstruck8]

It looks like the vendor’s pictures in artificial light. Here is late afternoon sun in the Pacific NW.

Your stone looks fascinating. I love the big bright yellow-orange eye in your third picture.

I'm wondering whether you are seeing the distinct orange and yellow blocks shown in the vendor's pictures. Or seeing the eye change colour between orange and yellow as it rolls over the surface when you tilt the stone. This is what made the stone seem special in the vendor's pictures - most rainbow moonstones have orange and blue, but this one seemed to have orange, yellow and blue.

 

[Starstruck8]

Hey guys!!! I am needing you guys opinion, one of my vendor send me video of this stone (since I dont know how to upload a video, so Im capturing the screenshot of the video).

Its a big stone, almost 16ct quoting at 450 per ct, and quite colourful under sunlight. However the sheen is not as strong as I would like it to be.

I was hoping that someone who has seen more of these stones than I would answer. But, FWIW, the picture on the back of your hand looks like the one good quality faceted stone I've seen - fascinating colours, but a bit weak, and not as strong as the colours of the 'eye' of a good cab. Are the best faceted stones better, or is yours par for the course? I don't know enough to say.

I have to say that the stills from the vendor's video look a bit overcooked (If the stone really looks like that, I'd be delighted.) The vendor pictures of the cab look a look a lot overcooked. But, allowing for that, it could be a fascinating stone anyway. I just don't know enough to say.

To show a video, you have to load it to a video hosting site (e.g. YouTube, lmgur, Vimeo), then use 'insert media' from the 'three dots' dropdown menu to link to it. You can see the acceptable sites in the box from the menu.

 

[LC2016]

Yes I have personally see the faceted stone, but since both day of my visit is a rainy day so the best picture i can take is with indoor light (its taken with some distance from the light source). Hence I attach both the pic taken by me under indoor lighting and vendor pic under good sunlight.

The vendor pic of both cab and faceted stone are screen capture from vendor video. Frankly speaking I do believe the faceted stone looks like vendor video under sun, since its normal that moonstone looks better under sunlight. Cant say much about the cab one, but thats one crazy pice and crazy cut.

Anyway it could be abit too late for me to try to acquire the faceted stone as it seems one dubai customer is also trying to buy this stone, so Im the second in line right now.

 

[LC2016]

I was hoping that someone who has seen more of these stones than I would answer. But, FWIW, the picture on the back of your hand looks like the one good quality faceted stone I've seen - fascinating colours, but a bit weak, and not as strong as the colours of the 'eye' of a good cab. Are the best faceted stones better, or is yours par for the course? I don't know enough to say.

I have to say that the stills from the vendor's video look a bit overcooked (If the stone really looks like that, I'd be delighted.) The vendor pictures of the cab look a look a lot overcooked. But, allowing for that, it could be a fascinating stone anyway. I just don't know enough to say.

To show a video, you have to load it to a video hosting site (e.g. YouTube, lmgur, Vimeo), then use 'insert media' from the 'three dots' dropdown menu to link to it. You can see the acceptable sites in the box from the menu.

I tried to upload the video on youtube and here it is!!
So first, this one stone is the stone i mentioned very early, the video from my local retailer. I havent seen the stone in person, but the video doesn't seem enhanced to me and this is the best, and expensive, stone I have seen (from video) so far.

Second, this is the faceted stone we talking about. First video is taken by vendor under sunlight and second by me under indoor lighting

Third is the ultra expensive “sugarloaf” moonstone from this IG vendor. I never purchased from this vendor so I dunno how accurate is the video.

View this content on Instagram

View this content on Instagram

But all in all I agree with you that for faceted moonstone, the light reflection is somehow competing with the sheen and weaken the sheen. Additionally, from my observation it looks like blue coloured sheen is stronger than the orange coloured one in general.

 

[Mrsz1ppy]

Your stone looks fascinating. I love the big bright yellow-orange eye in your third picture.

I'm wondering whether you are seeing the distinct orange and yellow blocks shown in the vendor's pictures. Or seeing the eye change colour between orange and yellow as it rolls over the surface when you tilt the stone. This is what made the stone seem special in the vendor's pictures - most rainbow moonstones have orange and blue, but this one seemed to have orange, yellow and blue.

I will take a video and post it.

 

[Starstruck8]

I said earlier that my little cab had only two basic colours, orange and blue. I suggested that other colours might be made by mixing these. I have now realized that there is another way rainbow moonstone can show a range of colours.

Here is an example:


The picture was taken with the stone in front of a row of windows. (The direct reflections of the windows can be seen as the light grey arc at the top of the stone. The dark lines are the reflections of the window frames.) The camera was looking down on the stone, a bit in front of it. See sketch at left.

Note that the colours are in rainbow sequence, from orange at the top to blue at the bottom. I'm pretty sure that all these colours are formed by schiller-reflection from the 'orange' schiller planes.

The trick is that the 'orange' schiller planes reflect orange when the light is square-on to them. As the light moves away from square-on, the reflection shifts to shorter wavelengths (i.e. towards blue). This is typical of colours produced by interference. You can see it in opals and iridescent pearls. Their colours are 'redder' when lit and viewed square-on, 'bluer' when there is a wider angle between the incident light and the viewing direction. For those who care, the wavelength shift factor is the cosine on the angle between the incident light and the normal to the schiller plane.

Here is a sketch of what I think is happening:


The schiller planes are shown in orange. (To keep the sketch readable, only one full ray path is shown. You can imagine all the others.) The sketch shows that when you are looking at the higher parts of the stone, you are looking at rays reflected at a smaller angle to the normal to the schiller plane. When you are looking at the lower parts, you are seeing rays reflected at a bigger angle to the normal. So the colours are shifted more towards blue. At least, that's my story... I've done the maths (which I will spare you) and it seems to fit.

@MrszIppy, This story does not seem to explain the yellow block in the orange in your stone:


It still seems that this block has a different 'square on' colour from the orange around it. Have you seen anything that might throw some light on this?

@LC2106, The first video you posted is totally fascinating, almost unbelievable. I encourage everyone to view it and be amazed. How is your search going?

 

[LC2016]

I said earlier that my little cab had only two basic colours, orange and blue. I suggested that other colours might be made by mixing these. I have now realized that there is another way rainbow moonstone can show a range of colours.

Here is an example:


The picture was taken with the stone in front of a row of windows. (The direct reflections of the windows can be seen as the light grey arc at the top of the stone. The dark lines are the reflections of the window frames.) The camera was looking down on the stone, a bit in front of it. See sketch at left.

Note that the colours are in rainbow sequence, from orange at the top to blue at the bottom. I'm pretty sure that all these colours are formed by schiller-reflection from the 'orange' schiller planes.

The trick is that the 'orange' schiller planes reflect orange when the light is square-on to them. As the light moves away from square-on, the reflection shifts to shorter wavelengths (i.e. towards blue). This is typical of colours produced by interference. You can see it in opals and iridescent pearls. Their colours are 'redder' when lit and viewed square-on, 'bluer' when there is a wider angle between the incident light and the viewing direction. For those who care, the wavelength shift factor is the cosine on the angle between the incident light and the normal to the schiller plane.

Here is a sketch of what I think is happening:


The schiller planes are shown in orange. (To keep the sketch readable, only one full ray path is shown. You can imagine all the others.) The sketch shows that when you are looking at the higher parts of the stone, you are looking at rays reflected at a smaller angle to the normal to the schiller plane. When you are looking at the lower parts, you are seeing rays reflected at a bigger angle to the normal. So the colours are shifted more towards blue. At least, that's my story... I've done the maths (which I will spare you) and it seems to fit.

@MrszIppy, This story does not seem to explain the yellow block in the orange in your stone:


It still seems that this block has a different 'square on' colour from the orange around it. Have you seen anything that might throw some light on this?

@LC2106, The first video you posted is totally fascinating, almost unbelievable. I encourage everyone to view it and be amazed. How is your search going?

Thanks for resolving the puzzle for us, the dedication is unmatched.

I end up buying that faceted stone and will post picture once I received it. In the meanwhile, I found this cute Indian rainbow moonstone, which despite being small (4.x ct), have an amazing glow. Attaching the vendor pic to showcase