16 



Case 49. Themn-nerous samples of diamantiferous wash are of interest. 



9163, 7653, 9250, and others, represent the pebbles associated 

 with the diamond. They comprise sajy^yJiire, topaz, zircon, quartz 

 (often jasperoid), and, in particular, a description of black 

 tourmaline, known as the pencil variety from its elongated form. 

 This is well shown in 9163. 



Like gold- and tin- bearing leads, the diamantiferous wash may 

 be overlain by a flow of basalt. 7715, a cavernous basalt con- 

 taining calcite, is such a flow from the Bingera field.* 



9250, near Bendemeer : a twin crystal. 



7318 : A small greenish stone from near Gunning. 



2128 : AV^ash from near Mittagong, where a few stones were 

 found, some years ago, in a small area of alluvial waiih overlying 

 the Hawkesbury Formation. 



The original source of the diamonds found in the alluvial 

 deposits of IS'ew South Wales, as in the case of the Indian and 

 Brazilian fields, is not certainly known ; but a recent discovery of 

 eclogite at Euby Hill, Bingera, appears to indicate the possibility 

 of this crystalline rock having been the parent-rock there, as is 

 believed to be the case in South Africa. It is probable that, 

 were the true home of the diamond to be traced, the stones 

 might be very sparsely scattered through it. 



The occurrence in rocks of igneous origin at Kimberley and the possi- 

 l^ility of artificially preparing diamonds throw much light as to 

 their probable origin. Tlie Kimberley occurrence is described on 

 page ]0i. The following notes on the artificial preparation of 

 diamonds will be of interest : — 



A French chemist, M. Moissan, considering that enormous pressure 

 M'ould assist the crystallisation of carbon, made use of the property 

 possessed by molten iron of expanding when it solidifies, t Moissan 

 tilled a very strong steel cylinder with molten cast-iron, and her- 

 metically sealed it. Not being able to burst the cylinder, the 

 expansive force of the solidifying iron squeezed the molecules 

 closer together, and compelled some of the carbon— which is 

 always present in cast-iron— to crystallise. On dissolving away 

 the surrounding metal wdth powerful acids, minute diamonds were 

 found among the residues. 



A German chemist has produced diamonds bj' simply stirring molten 

 olivine — a mineral fovmd in many igneous rocks — with a rod of 

 carbon. 



* There is no analo'jy, as is somstimes iniaorined, between this basilt cover and the 

 igneons rock constituting' tlie matrix of the Kimberley Diamond Field. (See yiajre lOI.) 



t Water has the same property. An old experiment wai to fill a bomb with water, plug' 

 up the openinsr, and p'aoe it in a freezing- mixture; in freezing, the water expands, 

 expelling the plug, or even barsting the bomb. 



