112 PROCEEDINGS OF THE ACADEMY OP 



teristics of the simpler compouncls which most resembk it, to 

 which of them it owed its morphological properties; and, having 

 decided this question, to write the formula, for that mineral as the 

 si^ecies, and consider the other as a complex variety of it, 



I append some few names of minerals with their old and new 

 rational formulas generally compared, and in addition to the usual 

 method of writing these new formulas I have added that form of 

 graphic symbol which presents fewest typographical difficulties. 



Old Formula. New Formula. 



Niccolite. 

 NiAs Ni^^As^ As^=:Ni"or } .^. 



As"^ = Ni'^ Ni^^EEAs'" 



Breithauptite. 



NiSb (NiJ^'^Sb./" 



NigSb, 



Bornite. 



(Cure)S (Cu,)3"fS,"i(re,)'^ 



(Cuj3"FeJ^S, 



(Eecalculated from one of the 

 original records of analysis.) 



Chalcop3'rite. 



Cu.^S + FeS+FeS, (D) {Cu.y'=S,''=FeJ'=S^'\ 



usually Cu.S + Fe.Sg ' (Cu,)"Fe/^S, 



Barnhardite. 



2CuS+FeS+FeS, (Cu4"=S^" = Fe.7i=S 



(CuJ,Fe,S, ' 



Calaverite. 



Au,Te^ Te"=An"^ Te" Te" 



Au"^=Te" 



Au"n^e.," Te/'Au"^ 

 (AV"Te,"), ' 



Miargyrite. 



Ag,S+Sb,S3 Ag^ S" Sb"i=S" 



Ag^Sb"^S, 



^.IC-I-vIIIli^ 11 



