OX CORDIEIUTE AS CONTACT MINERAL. 325 



parallel to the Brachypinacoid (010), like those obtained on the Cor- 



dierite of Laach bv Hussak.* 



j 



Chemical Composition, — Some difficulty was experienced in 

 collecting a sufficient quantity to serve as a pure sample for chemical 

 analysis. Fragments of transparent portions were cautiously picked 

 out by hand from The larger crystals, having the characteristic 

 structure already described, as it was often difficult to distinguish 

 these from Quartz-grains found in the slate. The black carbonaceous 

 particles were avoided as much as possible. Fragments thus collected 

 were washed with dilute hydrochloric acid, to remove the coating of 

 iron hydroxide. Examined under the microscope, the sample was on 

 the whole pure, but very small dusty aggregates of carbonaceous matter 

 were generally attached to the fragments. It was also almost impossi- 

 ble to get the sample absolutely free from the beginning of the altera- 

 tion which, even in fresh-looking transparent specimens, had set in from 

 the very fine fissures. The analysis of the sample thus selected, was 

 kindly conducted by Mr. T. Shimidsu, with the following result : — 



SiO, 48-43 7 



Al/L 32-36 



L',0 8'55 



MnO 1-32 



CaO -46 



MgO 7-81 



Tl,n , 1-55 



100-48 

 Water must be ascribed to the beginning of the alteration. 

 Manganons oxide is partly due to the fine platy enclosure already. 

 alluded t<>. 



* 1. c. p. 355. Tafel. II. fig. 28. 



