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.