Zircon

I have noticed that there is a little confusion on the refractive indices of zircon on the web. Mindat lists: nω = 1.925 - 1.961 nε = 1.980 - 2.015 but other sites state nω and nε in reverse order (e.g.: [webmineral.com] ). Could somebody knowledgable comment on this?

Branko

Hi Branko,

Mindat data is correct. Since Zircon is tetragonal, it is uniaxial, that is with a single optic axis. Also, since ε is greater than ω the optic sign is (+). This should be true in all cases. Only when when Zircon is metamict can it show some biaxial characteristics but minor only and e' (ε-ω) should still always be positive never negative. Mindat uses the same optical data for Zircon as is listed for Zircon in Handbook of Mineralogy.

Ron

Ron,

thanks! If the indices of refraction were as stated on webmineral.com, zircon would be optically negative, which is in fact what they claim. So that alone is no clear indication on who is right and who is wrong. But I tend to believe Mindat, because it is almost always correct. The Handbook of Mineralogy is another indication on that.

Branko

Ron is completely right.