NEW CALEDONIA NICKEL ORES. 59 



by the large amount of silica it contains, generally as minute 

 glistening crystals of quartz, or in the amorphous condition. The 

 magnesia ore contains only a small quantity of quartz, but a very 

 considerable amount of magnesium silicates, and has a paler green 

 colour than the former. The brown ore is the least common variety, 

 is -very soft, and as a rule contains only small quantities of quartz 

 and magnesia, but much ferric oxide. Generally speaking, however, 

 they are classified into the green and the brown minerals. 



From time to time analyses of the ore have been published, 

 leading to a variety of formula? with this feature only in common, chat 

 it is a hydrated silicate of nickel, in which the nickel is replaced to a 

 greater or lesser extent by magnesia or oxide of iron. Perhaps the 

 various complicated and somewhat contradictory formulae devised 

 may be accounted for by the difficulty in obtaining pure pieces, and 

 that the finely intermixed quartz may have escaped observation, thus 

 giving a percentage which does not truly represent the combined 

 silica, but rather that of silica + quartz, for pieces of the ore which to 

 the eye appear thoroughly homogeneous in the great majority of 

 cases give an amount of insoluble silica varying from 2 to 10 per cent. 

 Nevertheless, I have frequently observed that those ores containing 

 much magnesia give differences in analysis which do not agree 

 relatively to any distinct formulae, but seem rather to indicate a 

 mixture of silicates ; as, however, the magnesia diminishes, these 

 differences are gradually reduced, and the composition then becomes 

 more constant, and more closely complies with the calculated 

 numbers, except for the combined water, for which ] have been 

 unable to find a constant factor. Having excellent opportunities 

 for procuring pure specimens, and from the many hundreds of 

 analyses made of the same, there seems to be no doubt that both 

 kinds of ore approach very nearly to hydrated sesqui-silicates of 

 nickel giving a formula of 7 NiO, 6 Si0 2 , x H„0, part of the nickel 

 in the green ore being replaced by magnesia, oxide of iron, or 

 alumina, the magnesia predominating, whilst in the brown the oxide 

 of iron is in excess. The following carefully executed analyses of 

 both ores give only the amount of soluble silica, as in those cases 

 when quartz was present it has been calculated out : — 





I. 



II. 



III. 



IV. 



V. 



VI. 



Si0 2 



35-55 



36-24 



35-25 



3478 



35 'SO 



20-57 



NiO 



48-38 



44 94 



46-30 



43-79 



43-54 



15-56 



MgO 



5-02 



8-75 



— 



2-75 



2-65 



0-81 



F ei 3 



1-41 



0-21 



9-00 



6-30 



1073 



49-03 



A1. 2 3 



1-09 



1-03 



— 





— 



— 



Cr. 2 3 



0-15 



— 



014 



— 



— 



3.82 



MnO 



— 



— 



— 



— ' 



019 



trace 



H 2 



8-85 



8-98 



9-20 



12-40 



8 00 



10-32 



100-45 100-15 99-89 100-02 100-91 100-11 



Nos. I and 2 represent the composition of the green ore. The colour 

 is a fine brilliant grass-green. Hardness, 2-3. Specific gravity, 3-00. 

 Streak light green, waxy lustre, and slightly translucent at the thin 

 edges. Before the blowpipe the colour darkens, becoming dark olive 

 green ; in presence of much ferric oxide, red. 



Nos. 3, 4, 5 and 6 give the composition of different brown ores. 

 The colour varies from light brown to a deep sometimes slightly 

 translucent chocolate ; streak yellow or brownish yellow ; the fracture 



