On tJie Occurrence of the Diamond near Mudgee. 103 



Griving an average weiglit of •23 carat each, or close upon a carat 

 grain. The largest diamond hitherto discovered in this locality 

 was a colourless octahedron, weighing 5| carats ; it was found in 

 the river, between Two-mile Flat and the Eocky Ridge, at a spot 

 where the Older Pliocene drift had been discharged in gold- 

 washing. 



During the first five months of systematic washing over 2500 

 diamonds were obtained, and several thousand more have been since 

 collected. They are mostly pellucid and colourless ; many have 

 a straw-yellow tint, and tints of brown, light or dark green, and 

 black r.re more rarely met with. An opaque black one has been 

 found, and another of a dark green colour, with the external 

 appearance of having been rubbed with black lead. Black specks 

 within the crystal are not uncommon. The specific gravity taken 

 from a number of crystals is 3'44. They all show a well-defined 

 crystalline form, though irregularities of development are frequent. 

 It is very rare to meet with worn or fractured specimens. They 

 are easily recognised by their characteristic lustre, which is never 

 impaired by a superficial coating of foreign matter. Sometimes 

 they are dull, but this is not due to water- wearing or incrustation, 

 but to multitudes of minute angles and edges of structural 

 planes, which give a frosted appearance to the crystal. The 

 forms met with are the octahedron, twin octahedron, dodecahedron, 

 tris- octahedron, and hexakis-octahedron ; the two latter are 

 frequently hemihedral, with curved faces, and are sometimes 

 developed into flat triangular twins. One specimen of the 

 deltoid dodecahedron has also been found. The curious 

 flat triangular twin-crystals are derivable from the tris- 

 octahedron. If we regard the latter as an octahedron, with 

 a low triangular pyramid on each of its faces, and out 

 of the eight pyramids we imagine that only two, corresponding 

 to opposite and parallel octahedral faces, are developed, on 

 applying these two pyramids together, they would not form a 

 closed figure, but by twisting one 180° round, we form the 

 triangular t-nan crystal. Or simpler, if we inspect a twin 

 octahedron, there are but tw© of the original triangular faces 

 entire ; these are opposite and parallel, and by replacing these 

 two faces by the corresponding planes of the tris-octahedron, the 

 rest of the faces of the twin octahedron may be obliterated, and 

 thus the triangular crystal will result. The structural laminae 

 are very distinct on some crystals, and many of the octahedrons 

 show these successive layers of growth in a very beautiful 

 manner. 



The fluctuating yield, small average size of the gems, great 

 expense in extracting the drift from beneath the basalt, cartage 

 to water, and washing effectually, are the drawbacks which have 



