What produces the colour in opal

Optical Properties of Solids, Oxford University Press, Oxford. 

Heavens, R.W. Ditchbum, 1993, Insight into Optics, John Wiley Sons, Chichester, Sussex. 

The properties of fight with respect to colour are found in  

Nassau, 2001, The Physics and Chemistry of Colour, 2nd edn, John Wiley Sons, Chichester, Sussex. R.J.D. TiUey, 2000, Colour and the Optical Properties of Materials, John Wiley Sons, Chichester, Sussex. 

A series of articles on photovoltaics is to be found in Materials Research Society Bulletin Will (October 1993). 

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