http://www.rauantiques.com/product.asp?InvCategoryID=7&page=1Golconda Diamonds
http://www.rauantiques.com/product.asp?InvCategoryID=7&page=1
Golconda diamonds are a pale pink colour caused by the presence of isolated nitrogen atoms situated next to vacancies in the crystal structure.
The combinations of impurities and/or defects that cause colour are termed colour centres. Diamonds with more than one colour centre often appear brown; however the exact nature of colour centres has yet to be determined in many cases. For example, violet diamonds have been discovered in Australia. These are known to be rich in hydrogen and so the colour centre is assumed to be related to hydrogen, but little more than this is known at the moment.
Other Colours
Other colours are caused by different combinations of impurities and crystal defects occurring next to each other in the structure. This enables the crystal to absorb some wavelengths of light and not others.
BEWARE OF FAKES!
It is relatively easy to expose a weakly yellow-coloured diamond to radiation, thus causing it to change to a more desirable (and more expensive!) green colour. Various irradiation and heating techniques to increase the value of diamonds e.g. unwanted brown diamonds can be turned to aquamarine-blue colours which are far more valuable.