C. A. Ingersoll — Hemimorphic Widfenite Crystals. 195 



The pyramidal hemihedrism is shown by a series of stria- 

 tions, resulting from an oscillatory combination of n with one 

 of the adjacent e faces. This is found on all the crystals to 

 the right of n only. Moreover, the form ir is found only to the 

 right of e. This development of hemihedrism in the pyra- 

 midal forms of Wulfenite is particularly interesting, since it 

 has, hitherto, been observed chiefly in the prismatic zone. 



The calculated angles in the following table were obtained 

 from the fundamental measurement of Dauber,* w A w, lll^s 

 III = 131° 42', from which the length of the vertical axis, 

 e — 1*5771, is obtained. 



Us\7l 



e /^n 



U /\ u 



e /^u 

 e s^p 



■)ly\7t. 

 7Z S\7l, 

 TV \7t. 



111^111 



101^101 

 101^111 

 102^102 

 101 /O 02 

 201^201 

 101^201 

 101/s313 

 111/^313 

 313^313 

 313^313 



Measured. 



80° 



25' 



115 



16 



40 



12 



76 



20 



19 



20 



144 



31 



]4 



42 



15 



42 



24 



30 



117 



56 



62 



8 



Calculated. 



80° 



22' 



115 



15 



40 



11 



76 



31 



19 



22 



144 



50 



14 



47 



15 



43 



24 



28 



117 



56 



62 



4 



In the above table the measured angles have been taken as 

 the mean of four readings. No accurate measurements could 

 be made on c, owing to its vicinal development. The occur- 

 rence of the new forms p and iz is proved not only from 

 the above measurements but from their positions in the correct 

 zones. 



It is probable that the isomorphous minerals, scheelite, 

 powellite and stolzite are also hemimorphic ; but as yet no forms 

 have been observed which indicate this. 



In conclusion the author wishes to express his thanks to 



Professor Penfield for assistance rendered during the course of 



this investigation. 



Laboratory of Mineralogy and Petrography, 



Sheffield Scientific School, April, 1894. 



* Pogg. Ann., cvh, p. 267, 1859. 



Am. Jour. Sci.— Third Series, Vol. XLVIII, No. 285.— Sept., 1894. 

 13 



