Palache and Warren — Krohnkite, Natrochalcite. 343 



Phase a. — Clusters of octahedroid crystals of the type of 

 figure 1 but mostly in twin groups, the crystals firmly aggre- 

 gated to a highly cellular mass, largely infilled with an earthy 

 yellow iron sulphate which may be copiapite. These crystals 

 reach a diameter of l*5 cm and are of a dull greenish blue 

 color with smooth but lusterless faces. 



Phase h. — Single crystals and fibrous or acicular aggregates 

 of pale blue color, implanted on the white quartzose vein 

 material. The crystals are slender prisms with the forms of 

 figure 1 but with the prism largely developed and its planes 

 much curved and facetted through the presence of steep vicinal 

 pyramids. Single crystals reach a length of 4 cm . 



Phase c. — Solid crusts up to 2 cm in thickness of deep 

 vitriol blue color, the crystals composing the mass often large 

 and either short or long prismatic, with the forms of figure 2. 

 In cavities on the surfaces of such crusts is a second generation 

 of prismatic crystals of pale blue color, beautifully crystallized 

 and showing the complex combinations of figures 3 and 4. 

 Twin crystals of the type shown in figure 5 are also found on 

 this deep blue material. 



The position adopted for the crystals differs from that given 

 by Dana, front and back being interchanged. The axial ratio 

 calculated from measurements on a number of crystals is 



d lb :c= 0-5229 : 1 : 0-4357 (3 = 56° 11' 20" 

 The observed forms are as follows :— #(100), 5(010), m(110), 

 A(120), £(130), *(011), d(021), /(031), t (101), ^(302), 0(3.01), 

 p0.ll), /-(121), #(111), <121), io(5ll), a<221), 2(331), *(561), 

 0(10-10-1), 2/(232), »(I32). 



(Tables of measured and calculated angles and combinations 

 will be found in the paper cited above.) 



Twinning. — The twin plane is the base, (001). Twins 

 are either contact or interpenetrating, the latter resembling 

 parallel growths owing to peculiarities of angles and distortion. 



