360 M. Walmstedt's Resean/ws on 



Oxygen. 



Silica 40-83 , . . 21-23 



Magnesia 47-74 . . . 18-48\_2j.j, 



Protoxide of iron 11-53 .. . 2-63 J 



Protoxide of manganese . . 0'29 



Traces of lime 



Traces of alumina 



100-39 



Olivine from Somma. 



Two quantities of this were analysed, one consisting of 

 1-684 gr., the other of 1-9435 gr., and the following are the 

 results : 



1st Anal. Oxvgen. 2nd Anal. Oxygen. 



Silica .... 40-08 .... 20-84 40-16 21-88 



Magnesia . . 44-24 17*13 i 44-87 17-37 1 



Protoxide of 1 J- =20-60 > =21-87 



l-iotoxKleot I ^,.26 3-47) 15-38 3-50 J 



n-on J 



Protoxide of 1 ^.^^ q.^q 



manganese J 

 Alumina ... 0-18 0-10 



100-24 100-61 



According to these analyses, the composition of olivine'may 

 very well be expressed by the formula p | S or fr Si\ sup- 

 posing that R indicates the class of isomorphous bodies to 

 which magnesia and protoxide of iron belong. If we further 

 compare with this the known analyses of chrysolite, which, 

 as I stated, correspond with the same formula, it seems esta- 

 blished also by chemistry that chrysolite and olivine must be 

 considered one and the same mineral, their chemical relations 

 being the same, and their integral nature being susceptible of 

 expression by the formula which I have proposed. 



It is well known that olivine often has a marked tendency to 

 disintegrate. In oi'der to trace the cause of this more closely 

 I examined some disintegrated olivine from the top of the Wil- 

 helm at Cassel. Its colour was a rusty yellow, its lustre and 

 transparency had disappeared; but its cohesion, although di- 

 minished, still prevented it from crumbling to powder. In 

 the interior of one part of the grains the disintegration had 

 not proceeded so far; so that the colour, although it was already 

 turning very much to yellow, still preserved a mixture of 

 gi'een : there might also be perceived more or less transpa- 

 rency still, as well as lustre, but this was changing to a dirty 

 appearance. 



The 



