Prof, B. Silliman 0}i some American Miiierals. 463 



" Boltonite," as giving the supposed chemical constitution of 

 this substance. 



It will presently be shown that there is every probability 

 that Dr. Thomson applied the name bisilicate of magnesia to 

 another substance ; and that the boltonite of Prof, Shepard is 

 not the substance which he analysed. 



Having received specimens of boltonite from Mr. Saemann, 

 a very intelligent and discriminating mineralogist from Berlin, 

 I was induced to undertake an analysis of it, which gave me 

 the following results. The specimen analysed was the yellow 

 variety. 0*5753 grm. of substance gave — 



Oxygen. 



Silica .... 46-062 = ... 23-23 = 8'" 



Alumina . . . 5*667 ... 2-64 1 



Magnesia . . . 38-149 14*76^ 



Protoxide of iron 8*632 1*95^ = 17*14 6*.' 



Lime .... 1-516 0-43 



100-026 

 Formula SSiO^ 1 Alt)^ 18MgO = 2RO, (SiO^, Alt)^), or 

 2(MgO, CaO, FeO), (SiO^, AW). 



8 atoms Silica . . . =370-08 = 46-556 per cent. 

 1 atom Alumina . . 51-47 6-372 



18 atoms Magnesia . 372-66 47*072 



794-91 100-000 

 If we consider the alumina as not an essential constituent of 

 the mineral instead of replacing a part of the silica (a view 

 which I am not disposed to take), then we shall have a silicate 

 of magnesia and the other bases, whose formula will be 

 9RO, 4Si03. 

 Referring to Thomson's analysis and description of his bi- 

 silicate of magnesia, we read {loc. cit. p. 50) that the mineral 

 received by him from Mr. Nuttall (from Bolton, Massachus- 

 setis) bears so much resemblance to the picrosmine of Hai- 

 dinger, both in character and composition, " that he strongly 

 suspects the two things to be mere varieties. The mineral is 

 white, with a shade of green ; powder white. It cofisists of a 

 congeries of prismatic crystalSf very irregularly disposed^ and 

 involved in each other. Lustre glassy; transparent on the 

 edges." The analysis gave — 



Silica 56-64 



Magnesia . . . 36-52 



Alumina .... 6*07 



Peroxide of iron . 2-46 



101'69 



