f/'or/i the Ncwhtnds Diamond Mines, Griqualantf West. 483 



(4.) Residue from the I)inwntiferoux Edofjitc. 



After the reading of my description of the " diamantiferous eclogite," 

 Sir YY. Crookes kindly offered to examine that rock for microscopic- 

 diamonds. Taking one of the fragments, weighing 130'5 grammes, which 

 had been detached in slicing the specimen, he treated it as follows : 

 " After being very coarsely broken up, the material was put into a 

 very strong sulphuric acid. The acid was boiled for some time, and, 

 after being allowed to cool, the residue was washed, dried, and then 

 heated for some hours in strong hydrofluoric acid. After it had been 

 well washed and dried the treatment with hot sulphuric acid was 

 repeated. The mass, after a few alternations of these acids, became 

 disintegrated, and all, except a few crystalline lumps, were dissolved. 

 After about ten treatments only a few small crystals remained, and 

 these (with the exception of a sample) were reduced by a few more 

 boilings with the acids to a single small one about half a millimetre in 

 diameter." This was boiled fourteen times in each acid, and appeared 

 to l>e slightly reduced in size. " It sinks in methylene iodide, specific 

 gravity 3'35." This was sent to me with some of the small crystals just 

 mentioned, all being mounted. The solitary survivor of the whole 

 treatment showed on one side curved crystal faces, but on the other 

 appeared imperfect. These faces, so far as I could judge, indicated an 

 isometric or possibly a rhombohedral mineral. Its refractive index is 

 high, the colour a pale smoke-brown, and it apparently produced some 

 effect on polarised light. -That, however, was not conclusive, for 

 diamonds from Newlands, as at Kimberley, are often in such a state 

 of strain as to be anisotropic. Of the survivors of the first treat- 

 ment, the more abundant were colourless, rough in outline, but possibly 

 showing one cleavage surface, apparently at right angles to an optic 

 axis ; polarisation tints bright ; the refractive index high, but inferior 

 to that of a diamond. It appeared to me not improbably corundum. 

 The less abundant granules were more rounded in outline, with rather 

 rough, possibly corroded, surfaces, translucent, of a resin-brown colour, 

 apparently producing some effect on polarised light; on the whole 

 they seemed to bear some resemblance to rutile. But to come to any 

 conclusion about the first mineral it was necessary to detach it from 

 the mount. As I have no apparatus for very delicate work, that not 

 coming within my usual line of study, I had recourse to Mr. L. Fletcher, 

 the Keeper of Mineralogy, and Mr. L. J. Spencer, also of that Depart- 

 ment, at the British Museum. The latter attempted to measure the 

 supposed diamond with the goniometer ; the faces, however, were too 

 curved for the purpose, but both of them regarded the edges as too 

 sharp for the mineral to have suffered appreciably from the acid, as Sir 

 W. Crookes was inclined to think. They consider it to l>e really iso- 



2 M 2 



