MINERALS OF ECONOMIC VALUE, 



NEAV SOUTH WALES. 



GEMSTONES. 



[Note. — The colleetion of gemstones is by no means a satisfactory one, 

 partly due to the Museum having suffered heavily from burglary.] 



Crystallised carbon : As is well known, the diamond is charac- Case 49. 

 terised by its great hardness (H=10) and brilliancy. Crystals Diamond, 

 are characterised, by curved faces. The most common crystalline 

 form is that of an octaliechwn, on the faces of which low three- 

 sided or six-sided pyramids are frequently built.* 



The diamond sinks in heavy liquids. f 



Diamond Crystals. 



Diamonds have been found in numerous alluvial deposits in 

 ISTew South Wales, but iu the vicinity of Bingera and of Inverell 

 alone have tb.e deposits as yet proved of any commercial im- 

 portance. The stones are small in size, but of great hardness. 



7363, 2291, 2292, respectively from Eound Mount and Boggy 

 Camp, Inverell, show diamonds still embedded in the alluvial 

 washdirt. 



* Clear quartz cr3'stals are not infrequentlj- mistaken for diamonds ; their crystalline 

 form is, however, so very different (page 132) that the distinction between them is easy. 

 Moreover, quartz floats in heavj' liquids. 



t Heavy Liquids. — A number of liquids can be obtained of such a density as to permit 

 certain minerals to float, in the same way as wood does in water ; while others sink by 

 reason of their greater density. This affords a most valuable means of distinguishing many 

 minerals. Two of these heavy liquids that can be procured without difficulty, and used 

 without risk, may be mentioned, viz., boro-tungstate of cadmium (known as Klein's Solu- 

 tion), and methylene iodide. Hornblende will float in either of these when the density 

 is near its maximum. 



