THE PROSPECTOR'S HANDBOOK. 



In South Africa the diamondiferous alluvial deposits consists 

 chiefly of nodules of granite, basalt, sandstone, &c., and in 

 it are garnets, jasper, agates, pebbles (streaked with a suc- 

 cession of parallel rings) whose specific gravity is the sumo 

 as that of the diamond, &c. : so, too, in East Indies, &c. 

 Diamonds are often associated in river diggings with topaz, 

 garnet, zircon, spinel ruby, native gold, tinstone, &c. 



At the Kimberley mine, which, more or less, represents 

 others in the neighbourhood, the diamondiferous ground 

 forms a " pipe " or " chimney," surrounded by formations 

 totally different to the payable rock. The encasing material 

 is made up of red sandy soil on the surface, underneath 

 which is a layer of calcareous tufa, then yellow shale, then 

 black shale, and below this, hard igneous rock. The 

 diamond-bearing ground consists of " yellow ground " (really 

 the decomposed "blue ground"), which is comparatively 



FIG. 42. 



FIG. 43. FIG. 44. FIG. 45. 



USUAL FOBMS OF DIAMONDS. 



FIG. 46. 



friable ; and, deeper down, the " blue ground " (hydrous 

 magnesian conglomerate), which needs blasting by dyna- 

 mite. The " blue ground " is of a dark bluish to a greenish 

 grey colour, and has a more or less greasy feel. With it are 

 mixed portions of boulders of various kinds of rocks, such 

 as serpentine, quartzite, mica-schist, chlorite-schist, gneiss, 

 granite, &c. All this " blue ground " has evidently been 

 subjected to heat. The gems are in the matter which binds 

 together these rocks, not in the rocks themselves.* A dia- 

 mond-bearing "blue earth" formation occurs at Wajra 

 Karur, India. Diamonds are also found in Eussia, America, 

 various parts of Australia, New Zealand, Borneo, &c. The 

 method of detecting the diamonds is the same in principle 

 everywhere. The big stones are thrown aside, and the 

 smaller matter is washed and examined for diamonds. 



* Garnets abound in the " blue ground," also grains of black 

 carbou, magnetite, kyanite (blue), and a light green mineral occur. 



