N. L. Bowen — Cacoclasite from Quebec. 441 



Composition of Cacoclasite (Genth). 



Mols. Calcite Apatite Kest. Eatio. 



H 2 



1-04 





C0 2 



6-73 



•153 



Si0 2 



31-52 



•523 



P 2 5 



2-19 



•015 



A1 2 3 



17-34 



-170 



Fe 2 3 



0-51 



•003 



MgO 



tr. 





CaO 



40-95 



•729 



Na 2 



tr. 





K 2 



tr. 





a In el. 



CaO — CaF 2 . 





153 



•015 



523 302 



1-00 



•170 1 

 •003 5 



153 050a -526 3-04 



The material analyzed by Genth was evidently, grossu- 

 larite 78-8 per cent, calcite 15-3 per cent and apatite 5-2 

 per cent. Believing that his tests indicated the presence 

 of free quartz, Genth decided that it was a mixture of 

 quartz, apatite and calcite with an indefinite mixture of 

 other minerals. It is worthy of note that Haines' analy- 

 sis likewise shows a ratio Si0 2 : A1 2 3 of almost exactly 3. 



Genth's "best" material evidently corresponds exactly 

 with the best material powdered for microscopic exami- 

 nation. In the case of Genth 's analysis No. II on poorer 

 material, it is necessary to assume that it represents, 

 besides the three above constituents, about 7 per cent 

 kaolinite and 2 per cent tremolite, both of which are to 

 be found on microscopic examination of cacoclasite into 

 which crystals of other minerals project. They are com- 

 monly tremolite needles, sometimes changing to talc and 

 prisms of scapolite (?) altered to kaolin. In no case 

 does the microscope reveal the presence of quartz and it 

 can only be assumed that the method adopted by Genth 

 of distinguishing free silica from the silica of a silicate 

 was not to be relied upon. 



Genth expresses the opinion that cacoclasite is second- 

 ary after scapolite. This conclusion is hardly borne out 

 by the measured values of the angles. While occasion- 

 ally prismatic, cacoclasite usually has the appearance of 

 a cubo-octahedron. Its departure from isometric sym- 

 metry is not obvious and it is necessary to measure the 

 angles before it becomes apparent. The faces are always 

 rough, with an eroded appearance and a peculiar glazed 

 surface. Frequently, they are distinctly concave. By 

 placing a drop of oil on a face and covering with a cover 

 slip, one obtains*a plane parallel to the face and capable 

 of giving a good reflection. Using this method and 



