Historical opal literature - an extract from Dana's Mineralogy
The following pages are an extract from this more historical text book of mineralogy. Written in 1962 it provides an window into the thinking and knowledge of the time, it is provided here as an example of mineralogical thought prior to the discovery of the structure of precious sphere type opal as revealed only two years later in 1964 by Australian Scientists, Segnit, Jones, Gaskin and Darragh. It may be considered that this is most likely the best up-to-date description of the mineralogy of opal for its time.
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