On the Chemical Composition of some Chilian Minerals. 103 



rocks. By that agency alone, exerted during the gradual emer- 

 gence of the main chain of the Pennine Alps, does it seem pos- 

 sible to explain such an operation as the hewing out of the stu- 

 pendous peak of the Matterhorn, whose origin must doubtless 

 have occupied his speculative faculties during those daring expe- 

 ditions that have so nearly led him to that summit which alone 

 seems able to defy the utmost efforts of the present race of 

 mountaineers. 



Pisa, January 3, 1863. 



XIII. On the Chemical Composition of some Chilian Minerals. 

 By David Forbes, F.R.S. §-c* 



T 



Hydrous Bibasic Arseniate of Nickel and Cobalt. 



HIS mineral, apparently a new species, occurs in veins in a 

 semi-decomposed greenstone or dioritic rock, which breaks 

 through the upper oolitic strata in the Desert of Atacama at 

 about twenty leagues to the eastward of the port of Flamenco. 

 The upper part of these veins contain it in abundance ; but after 

 a few yards in depth it appears to pass into chloanthite, from 

 which mineral it appears to have been originally derived. 



It occurs in fibro-crystalline masses, an agglomeration of cry- 

 stalline fibres united longitudinally ; colour greyish white ; lustre 

 non-metallic, dull up to silky or resinous ; streak non-metallic, 

 earthy; powder white; hardness 2*5. 



The specific gravity of three different specimens was respect- 

 ively as follows : 3*134, 3*069, and 3*054, consequently a mean 

 of 3*086. 



Before the blowpipe alone, upon charcoal in reducing flame, it 

 evolves water, changes colour, fuses imperfectly, and produces 

 metallic globules of a basic arsenide of nickel and cobalt, evolv- 

 ing at the same time arsenical fumes in abundance. In the oxida- 

 ting flame alone it is nearly infusible. With borax in the oxida- 

 ting flame it dissolves completely, forming a dirty brownish-blue 

 glass, owing its colour to the oxides of nickel and cobalt dis- 

 solved; in the reducing flame with borax it yields a bluish glass, 

 along with a metallic globule of basic arsenide of nickel and 

 cobalt. When heated in a closed tube, it does not decrepitate nor 

 change form, but evolves water and darkens in colour, becoming 

 then of a dirty greenish- or brownish-grey colour ; in open tube 

 it gives the same reactions. 

 Upon analysis, the following percentage results were obtained: — 



* Communicated by the Author. 



