Experimental evidence that oxygen is the principal impurity in natural diamonds

IN virtually all treatments of the physical properties of natural diamonds, nitrogen is considered to be a major impurity and is used to explain many properties (see ref. 1). This is true because of the analysis of ref. 2 where a good correlation between nitrogen concentration and optical spectra was found. Those results were obtained from the conversion of diamonds to graphite in a carbon crucible. The report that nitrogen is the major impurity in type 1 diamonds can be tested indirectly and qualitatively by analysing occluded gases released by crushing such diamonds. Numerous experiments in this laboratory on diamonds from Africa, North and South America have failed to show that nitrogen is the major impurity in natural diamonds 3,4 and we decided to reinvestigate the composition of gases released by the conversion to graphite of natural diamonds. We found oxygen and hydrogen to be the major impurities, and nitrogen to have only a minor role.