greenzaku on DeviantArthttps://www.deviantart.com/greenzaku/art/Iolite-changing-color-143766672greenzaku

Deviation Actions

greenzaku's avatar

Iolite...changing color

By
Published:
2.3K Views

Description

1.5cm, locale unknown (most likely India)

The upper and lower pictures are of the SAME STONE, a drilled bead, pictured at different angles under exactly the same lighting conditions. This fascinating change of colour that occurs when the stone is viewed at different angles is known as ' pleochroism ' and is caused by the 'double of refraction of light of a mineral.

Light of different polarizations is bent different amounts by the crystal, and therefore follows different paths through the crystal. The components of a divided light beam follow different paths within the mineral and travel at different speeds, and each path will absorb different colors of light. When the mineral is observed at some angle, light following some combination of paths and polarizations will be present, each of which will have had light of different colors absorbed. At another angle, the light passing through the crystal will be composed of another combination of light paths and polarizations, each with their own color. The light passing through the mineral will therefore have different colors when it is viewed from different angles, making the stone seem to be of different colors.'

- from Wikipedia [link]

Other examples of pleochroic minerals include tourmaline and sapphire. Iolite is an also known as Cordierite and is trichroic, able to change from bluish-purple to yellow-green to pale grey-blue depending on the angle that it is viewed. The change is so abrupt that supposedly, Viking navigators used thin pieces of Iolite to determine the sun's position on overcast days, although other sources contend that the stone used was actually Icelandic Spar, a doubly-refractive form of calcite. Both possibilities are outlined here:
[link] and [link]

The term used was actually ' sunstone ', but this is certainly not the firey orange gem sunstone known from elsewhere.

Large, grainy masses of Iolite are sometimes coated in wax or oils to improve the appearance and make them look more translucent. Because these are made of many tiny grains at different orientations, pleochroism is difficult to observe throughout such pieces.

More information on Iolite can be found at: [link]

It has been brought to my attention that in some East Asian shrines, artefacts and statues made of Iolite are rotated after prayer sessions and the colour change is attributed to divine intevention. While its not my place to deny a person's religious beliefs, the pleochroic nature of Iolite has a completely earthly explanation.

____________________________________

Yes! This image is FREE for non-commercial use as stock, reference or manipulation. Please Note me for commercial use or citation in scientific publications.
Image size
500x899px 48.78 KB
Make
Canon
Model
Canon PowerShot A480
Shutter Speed
1/125 second
Aperture
F/3.0
Focal Length
7 mm
ISO Speed
80
© 2009 - 2024 greenzaku
Comments20
Join the community to add your comment. Already a deviant? Log In
magpiesmiscellany's avatar
That is an awesome photo. I've heard of the effect, but never seen it this clearly. Normally I work with chips, so it just means some always look a dull brownish and the overall impact is lessened. The only faceted one I have never seems to show this.

I'm intrigued by the viking bit, but I've never found a good source for that piece of info.