Hi Steve
Natural green diamond is rare and many of the green diamond in the
market are mostly treated. Using basic gemological instrument to
identify the nature of colour is quite difficult, because of
improvement in technique of treatment i.e. irradiation plus
annealing.
I have learned from the Swiss Gemological Foundation Lab (SSEF,
Switzerland) and also Mr. George Bosshart (former chief gemologist
at the Gubelin Gem Lab) that you need to cool your diamond down to
minus 190 degree Celsius and use the UV visible spectrometer to
identify the presence of the presence of irradiated peak around 440
and 250 nm. Reference: Swiss Watch & Jewelry Journal 2/89.
You need to experience the technique involved in identification, it
is fun.
As for pricing, check with Christie’s auction houses, they sold some
green diamond before, quite high price.
Tay