[caryjames]

Hi guys- only one little wish. Particularly important to jewellery designers, gemmologists etc- Maxwell uses the Abbe number to determine a materials degree of dispersion.

In the gemmological world dispersion is always given a numerical value based upon the difference between the refractive index measured at the wavelengths represented by the so-called B and G Fraunhofer spectral lines. The B line (686.7 nm) is in the red part of the spectrum, while the G line (430.8 nm) is in the violet range. The higher the value, the greater the dispersion for the gem variety.

Some dispersion examples:

* Quartz: .013
* Tourmaline: .017
* Corundum: .018
* Peridot: .020
* Diamond: .044
* Cubic Zirconia: .066

These values are easy to find in any gemmological text whereas the Abbe number is just not available (anywhere that I can find) for any gemstone. If we could have the option of choosing between Abbe number and Dispersion number it would really help me out.

Thanks for letting me bend your ears !!