18-4 THE MINERALS OF NEW SOUTH WALES. 



quartz, topaz, magnesite and nodules of linionite which had been 

 set free from an impure magnesite, black vesicular pleonaste, spinel, 

 ruby, and osmo-iridium. 



The largest diamond found weighed 16 - 2 grains, or about 5| 

 carats. 



The average sp. gr. was 3*44, and the average weight of a large 

 number of those obtained was but 0*23 carat. (For further 

 particulars, see paper on the Mudgee Diamond Fields, by Professor 

 Thomson and Mr. Norman Taylor, in the Trans. Roy. Soc. 

 JST.S.W., 1870.) The total number found has been stated roughly 

 at about 6,000 ; the number also from Bingera must be nearly as 

 many — in all, say, 10,000 at least. 



In colour they vary from colourless and transparent to various 

 shades of straw, yellow, brown, light-green, and black. One of a 

 rich dark-green Avas found in the form of a flattened hemitrope 

 octohedron. 



The most common crystalline forms which have been met with 

 are the octohedron the hemitrope octohedron, the rhombic dode- 

 cahedron, the triakis and hexakis octohedron. The flattened 

 triangular hemitrope crystals are very common ; one specimen of 

 the deltoidal dodecahedron was met with. 



The lustre is usually brilliant or adamantine, but occasionally 

 they have a dull appearance. This is not due to any coating of 

 foreign matter or to the same cause as the dulness of less hard 

 waterworn crystals ; but it is owing to the presence of innumer- 

 able edges and angles belonging to the structure of the crystal ; 

 these reflect the light irregularly at all angles and give the stone 

 its frosted appearance. 



The diamonds at Bingera occur under almost exactly the same 

 circumstances as at Mudgee, and with the same minerals, except 

 that I did not come across either the black vesicular pleonaste or 

 barklyite. 



From a series of determinations made on nineteen of the Bingera 

 diamonds, I obtained a mean sp. gr. of 3*42. (For details vide 

 paper upon the Bingera Diamond Fields — Trans. Boy. Soc, N.S. W., 

 1873.) 



Diamonds have also been found at Bald Hill, Hill End, with 

 the same gems as at the above-mentioned places ; one octohedral 

 crystal, rather flattened, which I examined, weighed 9*6 grains 

 (troy) and had a sp. gr. of 3*58. 



A specimen of " bort" or black diamond w T as presented to me 

 by Mr. J. B. Peebles, of Sydney, which was obtained near 

 Bathurst ; it is of about the same size as a large pea, black in 

 colour, with a graphitic or black-lead lustre ; it is very nearly 

 spherical in form, but has a few slight irregular processes, which 

 seem to be due to an attempt to assume the form of the hexakis 

 octohedron. 



