686 



walker: hopeite 



forceps it fuses quietly to a clear glass, which is not yellow when 

 hot. 



Physical properties. The specific gravity, determined by 

 means of a solution of potassic mercuric iodide, is 3.03. Under 

 the microscope the crystals exhibit parallel extinction in the 

 prismatic zone. There are three cleavages corresponding to the 

 three pinacoids. The luster is vitreous except on the macro- 

 pinacoid, which is pearly. 



Crystallographic properties. The three crystals measured were 



similar as to habit and forms 

 present. The macropinacoid is 

 generally the predominant form. 

 The prism (120) is usually well 

 developed, while of the terminal 

 faces the most prominent are 

 the unit pyramid (111) and the 

 unit macrodome (101). The 

 other terminal faces are usual- 

 ly quite small, but, considering 

 their size, remarkable for the ac- 

 curacy with which they can be 

 measured. The measurements 

 on the two large crystals, while 

 satisfactory, are somewhat less 

 concordant than those obtained 

 from the third crystal, which is 

 only 2 mm. in length. The fol- 

 lowing forms were observed: 



Fig. 1. 



Hopeite from British 

 Columbia. 



(a) Pyramids (Ill) and (133) 



(b) Brachydomes (Oil) and (021) 



(c) Macrodomes (103), (101), and (201) 



(d) Prisms (670), (120), (5.11.0), (130), (3.11.0), and (160) 



(e) Pinacoids (010) and (100) 



The above list contains all the forms observed by Spencer 

 on crystals from Rhodesia except the pyramid (233). The form 

 (201) observed by Levy in 1837 on material from Aix-la-Chapelle 



