A'. S, Dana — Barium SulphaU from Perkins? Mill. <»i 



RO : Al.O., : l.l Si()., 

 •036 : '086 : "162; 



assuming this to be the case, and deducting tliis amount of 

 feldspar it would leave 



RO : SiO 



•789 : -77 1. 



which corresponds closely to enstatite. 



By calculating the soluble and insoluble parts as having been 

 determined on the original material minus the metallic portion 

 and water, and taking all the sulphur as representing troilite 

 (FeS), the general composition of the meteorite is shown to 

 be 



Metallic 2*23 



Troilite 5'03 



Soluble in acids . _, 39*84 



Insoluble in acids 52*42 



99-52 

 Laboratory U. S. Geological Survey, Washington, D. C, October, 1889. 



Akt. XIII. — On the Barium Snip], ate from Perkins* Mill, 

 Templeton, Province of Quebec; by Edward S. Dana. 



Some six months since M. A. Lacroix* described, under tbe 

 name of Michel -I evyte, a mineral having the same compo- 

 sition as barite, BaS() 4 - but as he believed crystallizing in the 

 monoclinic system. The discovery of the dimorphism of 

 barium sulphate is a point of so great mineralogical and chem- 

 ical interest that it seems necessary to scrutinize closely the 

 grounds upon which the conclusion rests. 



The mineral from Perkins' Mill is described as occurring in 

 masses showing three cleavages, two of them inclined to one 

 another at angles of 78° and 102°, and a third at right angles 

 to these — the geometrical form then, so far as known, is that 

 of normal harite. The cleavages, however, differ in kind : one 

 of those first named was found to be highly perfect, the sur- 

 faces having a marked pearly luster.: tin's is taken by Lacroix 

 as the orthopinacoid, //' (100). The cleavage corresponding in 

 position to the other prismatic face of barite was difficult; this 

 is taken as the base, p (001). The remaining cleavage, corre- 

 sponding to the base of barite, was intermediate between the 

 other two in character and gave surfaces having a vitreous lus- 



* Compter Rendus, cviii, 1126. 



