370 



C. H. Warren — Mineralogical Notes. 



001 /v 010 = 

 noi ^ no — 



001 /s 201 

 001 /s 111 

 001 a 111 

 010 ^ 110 



G A h = 



c A w = ooi a no = 



c /s 3/ = 001 a 110 



c ^ p 



6 /s m 



5 ^ Jf = 010 /s 110 = 

 ra y^M = 110 /s 110 = 



Measured. 



Calculated. 



86° 



85° 50' 



66 



65 53 



69 31' 



69 20 



80 48 



81 14 



54 20 



54 17 



59 (poor) 



57 52 



58 15 



58 4 



62 23 



62 26-J- 



59 32 



59 29 



The accompanying figures, 1 and 2, illustrate the habits of 

 the crystals. 



On the base of some of the better crystals a series of fine 

 striations can be seen, due to twinning after the pericline law. 

 The trace of the rhombic section can be seen in the striations 

 on the faces, m> 110, J/", 110, and 6, 010. A section cut from 



one of the crystals parallel to c, 001, when examined under the 

 microscope, showed a considerable amount of calcite and 

 other inclusions in addition to the flakes of graphite already 

 alluded to. Some of these inclusions are undoubtedly water, 

 as is indicated by the strongly marked, dark borders and 

 by the presence of a considerable amount of water in the min- 

 eral as shown by the analysis. The extinction measured on 

 the base, 001, using a Bertrand ocular and monochromatic 

 light, was —40°. 



A few of the smaller crystals were chosen for analysis. 

 The included calcite was estimated by determining the amount 

 of carbon dioxide evolved when the powdered mineral was 

 treated with hydrochloric acid, and calculating from this the 

 equivalent amount of calcium carbonate. After separating 

 the silica in the usual manner it was dissolved in potassium 

 hydroxide solution and thus separated from the small amount 

 of graphite, which was afterwards weighed on a Gooch cru- 



