Can't remember what this phenomenon is called...

[micellular]

What do you call it when there is a fracture in a crystal, which displays concentric rainbow lines due to interference? I vaguely recall it being eponymous like "__NAME__ lines", but I can't for the life of me remember what it is.

[rockjunquie]

Are you talking about an iris? Like in rainbow iris?

[micellular]

rockjunquie , I even misremembered the "lines" bit. I found it! They are called Newton's rings, and look like this. I also see it on the tables of my faceted gems against the glass tops of gem boxes.

[Deleted]

Jan 10, 2017 16:13:03 GMT -5 micellular said:

rockjunquie , I even misremembered the "lines" bit. I found it! They are called Newton's rings, and look like this. I also see it on the tables of my faceted gems against the glass tops of gem boxes.

Interesting. I have seen this effect on lids as you describe.

Knowledge is awesome. Thanks for sharing.

[Sabre52]

spectral display: When light dispersal through a prism show spectral effects. Or maybe "prismatic effect"...Mel

[metalsmith]

Newton's rings are from pressure, but I guess the fracture is causing a pressure differential, so yes. Nice pic btw, good example.

[Rockoonz]

I think iris is a bit different, but based on what I see from a friends huge collection of Montana agate iris I think the crystalline structure is very similar to Newtons rings. I wonder if the clear contra luz opals are related as well.

[Deleted]

I'm not sure that this would technically be a Newton's Rings phenomenon. It could be the thin film interference (TFI) effect in a conchoidal veil or fracture without being affected by any pressure. I've seen this on quartz quite a bit when there is a bit of moisture or other fluid trapped in a fracture causing the TFI. It sometimes disappears over time as the fluid evaporates or works its way out. Enjoying those "rainbows" by setting in full sunlight seems to accelerate the loss. Whatever the case, that certainly is a great photo.

Iris effect is a lens effect caused by very narrow banding creating grating diffraction. Both make rainbows. Opalescence (aka, color play) is caused by another grating effect created by light hitting the stacked spheres of cristobalite silica that make up the opal. Iris and opalescence are more closely related to each other than they are to TFI or Newton's Rings.

[adam]

Would the light from the bottom of a CD be called iridescence? The same light from a fracture in a quartz crystal?

[Deleted]

It is iridescence on the CD, but the specific method it is produced is similar to the diffraction effects you see in opals and iris agate: where the thin bands are close enough, they set up a grating that filters out only certain color wavelengths as the light is reflected back to your eye. Each color has a specific wavelength, and if the bands are very close together, certain wavelengths of light cannot be reflected directly back (or through). They interrupt light waves that are longer or shorter, and the colors associated with those wavelengths get deflected in directions other than back to your eye. That leaves only the colors/wavelengths that make it through the grating that you see. Since there are multiple bands, each one is at a different angle, so you see different colors making it back to your eye from different bands, which is why the colors shift as you move the CD and the banding in relationship to your eye shifts.

Thin film interference is more about the wavelength itself being altered as it passes through a transparent material and then bouncing from the other side of that material (be it liquid or solid) back to your eye. Depending on the angle, the light passes through more or less material which effects the wavelength returned. No grating is involved, and this is why oil and soap have iridescence.

Probably making it clear as mud?