gems, spinel, red, blue, violet, Ceylon, Sri Lanka

In his investigation of the absorption of red, blue, and violet spinels from Ceylon,¹ the author initially did not include the brown spinels, since an interpretation of the absorption curves appeared quite uncertain without any indications as to the nature of the colouring substance principally involved. The concluding discussion contained in the following paper,² on “The Colouring Substance of Natural Red, Blue, Violet, and Brown Spinels from Ceylon,” which could be undertaken on the basis of the photometric results obtained thus far and new analytical determinations, also provided the necessary indications for the brown spinels, so that their behaviour can now be discussed. According to these results, the principal colouring substance in the brown spinels is trivalent iron, with subordinate amounts of divalent iron and probably also chromium.