Talk:Pleochroism

Question: if double refraction splits into 2 beams at 90° angles polarized, and this leads to the dichroic effect; are trichroic stones split into 3 beams at what angles?

I wonder if you misunderstood. I think the author meant the two orthagonal (ie perpendicular, 90°) polarization states see different refractive indicies and thereby split into two paths. For a given wavelength, you should only be able to split it in two.

Question: Is this description of Pleochroism accurate? As far as i know, pleochroism is not only caused by a coloured gem or crystal,but by any mineral that has pleochroic properties such as biotite. does the name gem or crystal cover all minerals? Also, from how i read this article it seems that as the stage is rotated, the colours observed change for a mineral. this is the birefringence or the orientation at which the mineral is observed at under cross polarised light. Is pleochroism not the property of varying colour intensity within a mineral when the stage is rotated in plane polarised light? The author also makes it seem as though pleochroism is visible by the naked eye, is this not a phenomena that is only visible under a petrographic microscope? 203.160.127.213 04:04, 17 June 2007 (UTC)

This article definately needs improvement. The next contributer needs to have a deeper understanding. In part answer, you do not need a microscope, but it helps to see tiny crystals. This property could apply to any transparent substance, including minerals, it does not have to be a gem or crystal. I am hoping to see some good examples listed here, or more detail on how it is measured or described. GB 07:39, 27 June 2007 (UTC)

Examples of pleochroic minerals would be Really Good. Preferably with pictures. —Quasirandom 14:25, 15 August 2007 (UTC)


 * You can easily see pleochroism in some hand samples. It does not necessarily occur as varying intensity, but can actually be different colors.  Birefringence, I believe, is similar but is observed only in thin section.  If someone doesn't beat me to it, I might try to expand this article with examples. Professor Chaos (talk) 04:47, 12 December 2007 (UTC)

Some excelent examples to include, if you can find good slide images, would be a prismatic section of Tourmaline, with a strong pleochroic scheme of blue to pink, as well as biotite. These would clearly demonstrate that both variations in color intensity, as well as hue, are possible. A question for pleochroism in hand sample: If a mineral is pleochroic in thin section under PPL, will it neccesarily exhibit the same pleochroism under hand sample and non-polarized light? Boz3030 (talk) 07:55, 23 December 2007 (UTC) P.S: As to how it is measured or described: It is somewhat subjective in that it would be described as weak, moderate or strong pleochroism, generally with the pleochroic scheme given. My previous examples are strongly pleochroic, where a mineral like Epidote is an example of one showing weak pleochroism.

Common examples
What common gems or minerals display Pleochroism? Fred Talk 20:17, 6 September 2008 (UTC)


 * Russian version of this article lists Anatase, Dioptase, Kyanite, Topaz and Zircon among pleochroic minerals. But there is no valid links or any other kind of proof. This link mentions some as well. My own expirience with pleocroism if limited to trichriosm, but due to total abscence of any other expert... The most currently known example of natural trichroism (rare 3 sided pleochroism) is Tanzanite. Despite some claims to be the only mineral (or gemstone) to exhibit such effect, it is not. However it is often considered to have the strongest trichroic effect (unheated gems especially). The oldest known example of trichroism is probably Alexandrite. It's a bit strange, but both gems (Tanzanite and Alexandrite) change color, if viewing enviroment shifts from daylight to incandescent lightning. I'm cannot be sure if this effect is related to tricroism though. Some claim it is nothing but a coinscidence. 86.57.11.214 (talk) 18:26, 30 September 2008 (UTC)

Removed XPL pictures
I took the liberty of removing XPL (cross-polarized light) pictures that showed "pleochroism" which is a PPL feature, not an XPL feature. We certainly need a micrograph of this, preferably a GIF!  QFL 24-7 bla ¤ cntrb ¤ kids ¤ pics ¤ vids 04:36, 17 June 2012 (UTC)