CRYSTALLINE STRUCTURE OF GOLD NUGGETS. 73 
seen in the crystals, but the nugget was remarkably free from 
impurities, the dark parts are due to the way in which the light 
has been reflected from the surfaces of the crystals. Crystals 
which appear black in the photograph in one position, appear 
white or half-tone in another position. The whole of the surface 
was, of course, of a brilliant gold colour. 
When Plate 3 was taken this nugget had been by successive 
filings and etchings reduced to about 3 inch in thickness. 
The three preceding plates and No. 14 have been reproduced 
in collotype so as to permit of examination with a magnifying 
glass, the rest of the photographs have been reproduced by process 
blocks for the sake of economy, with unfortunately the loss of 
many details. None of the photographs or reproductions have 
been touched up or the effects heightened in any way. 
Tn Plate 4, there is a section of another nugget from Coolgardie, 
enlarged three diameters ; this nugget weighed 2-96 oz. Troy, and 
Was picked out of a large parcel of some hundreds of ounces 
mainly composed of nuggets from two to five ounces in weight, all 
, of which were only sub-rolled or water worn, and many pieces 
showed traces of external crystal planes. 
On etching this section with chlorine water its surface became 
thickly coated with silver chloride ; some of the crystals were 
much more rapidly etched than others—the lines of contact of the 
crystals were also deeply etched. Unless there be a difference in 
composition or of structure, the differential action of the solvent 
8 difficult to account for; in the case of meteorites we know that 
the characteristic Widmannstatt figures are largely due to a 
difference in composition. 
Freshly cut and thoroughly dried fragments of this nugget when 
strongly heated gave off water and sulphur dioxide, the latter — 
Probably due to the presence of a little iron sulphide, and it 
muitted an empyreumatic or nitrogenous odour similar to that 
_ Which I have often found to be given off by rock crystal, ey 
