Fieldspar · Optical Effects

Iridescence in Labradorite

I bought a Madagascan labradorite cabochon from Etsy a while back. I remember looking at the image online and thinking wow! I’ve got to have that stone. So when I opened the box to be presented with a drab, grey, semi-translucent stone I was a bit cheesed off. What I didn’t realise at the time as such a novice, is that the flashes of colour seen in a labradorite – an iridescent optical effect known as labradorescence – are directional and depend on the light hitting the stone just right. And actually, when I picked the stone up and held it under a bright light at an angle, the transformation was magnificent. From my grey stone popped electric blue-green and golden orange-yellow, all blended into a perfect little masterpiece of nature.

So why and how does this happen? Labradorite is composed of two different types of fieldspars – both with different chemical compositions (Na & Ca) – which are repeatedly twinned in layers called lamellar. If light enters the stone and does not encounter these layers, it remains dull and grey. However, when light enters the stone and encounters the layers it is diffracted. The normally white light is separated into its spectral colours, some of which interfere with one another or are cancelled out, while others are enhanced. The colour or succession of colours we then see are a result of this process of diffraction and interference.

Iridescent Optical Effect in Labradorite
The greeny-blue iridescent optical effect of labradorite, photo credit Tjarko Busink

The layered structure of labradorite, while responsible for such a beautiful display of colour, does make the stone less durable. Its toughness is poor with good cleavage in two directions, meaning careful handling is needed to make sure it isn’t broken in two. This is not a stone recommended for bracelets or cufflinks. And as movement is needed to show the optical effect, it is a better suited to drop earrings or rings than to pendant necklaces. Hardness on the MOHs scale is 6-6.5, so in addition to the cleavage, it will also scratch and chip much more easily than say a ruby or sapphire, so if you are wearing it in a ring, care is needed and a closed setting is best.

For me personally, labradorite is a wonderfully beautiful stone and I hope to add a faceted labradorite ring to my personal collection of jewellery soon. I mean, if this Etsy review is anything to go by, i’d be a fool not to.

A review of a labradorite ring from Etsy.

References & Credits:

Barbara Smigel – Optical Phenomena in Gemstones
GIA – Optical Effects of Phenomenal Cabochons

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