THE ORIGIN AND FORMATION OF THE DIAMOND. 169' 



out some years ago at Leipsic showed that, when some of the blue 

 ground from the South African Diamond Mines was taken and 

 melted in a furnace, and small diamonds were put into the melted 

 mass and retained there for an hour or so, the diamonds 

 were to a certain extent eaten away. On examining the residue 

 after the experiments, the diamonds were found to be eroded 

 to some depth from the surface, with little dark coloured balls 

 in the cavities, which were shown to consist of iron, or carbide 

 of iron, reduced from the oxide present in the blue. This result 

 is just what our chemical knowledge of these substances would 

 lead us to expect, and I think we have every reason to accept these 

 experiments as proving beyond doubt that the diamonds could not 

 possibly be kept in contact with the molten blue ground for any 

 length of time without being destroyed ; and, therefore, that 

 it was equally impossible that they could have been formed in 

 the molten rock. In certain metallurgical operations for the 

 production of wrought iron reactions occur similar to the Leipsic 

 experiments just quoted. Thus, for instance, at a certain stage 

 of the operations a given amount of the oxides and silicate of 

 iron is mixed with the molten cast iron. A lively reaction occurs, 

 resulting in the oxidation of the carbon in the cast iron at the 

 expense of the oxygen in the oxides of iron. This is quite anal- 

 ogous to the destruction of diamonds in the molten blue at the 

 expense of the oxides of iron contained in it. In other respects 

 also diamond, at high temperature, acts similarly to the other- 

 forms of carbon. Thus, for instance, if powdered diamond 

 is heated with powdered iron in a closed vessel to a temperature 

 of some 1,200° or 1,300° C, the iron is converted into steel, 

 just as if it had been heated with an equal quantity of graphite 

 or amorphous carbon. 



There is no need to pursue this j^oint further, especially as 

 the facts I am now about to mention with a view to determine 

 approximately the temperature at which diamond was formed 

 in the mud volcanoes, tell equally well against their formation 

 in the molten rock. 



I will now proceed to mention the facts I consider afford 

 sufficient proof that the diamonds in the South African Mines 

 were formed when the latter had reached the mud-volcano stage ; 

 and which also, I hope, will prove that the temperature at which 

 they were formed did not probably exceed a moderate red heat. 



A large number of diamonds have been found containing foreigii 

 enclosures of various kinds, gaseous, liquid and solid ; besides 

 which diamonds have been found crystallised upon, or adhering 

 to, other minerals, some of which, at least, can be melted at a 

 temperature not exceeding a moderate red heat. Certain dia- 

 monds have been found containing water, or containing mineral's 

 with water of crystallization or of constitution. Such a mineral; 

 apophyllite, was found some years ago in a diamond from De- 

 Beers Mine. It contains 16% of water, and on heating a portion 

 of the mineral obtained from the inside of the De Beers diamond 

 in a glass tube water was given off. The diamond was de- 

 clared by Mr. Gardner Williams to be perfect on the outside,- 



