PHYSIOGRAPHY. 71 



Blende. 



Brittle. Hardness = 3-5 ... 4-0. Sp. gr. = 4-078, a 

 cleavable variety; =4*027, a columnar, compound variety. 



Compound Varieties. Twin-crystals. Octahedral he- 

 mitrope. (fig. 50.) This composition is repeated, as in 

 fig. 61, and sometimes for a number of times. Reniform 

 and other imitative shapes : surface rough ; composition 

 columnar, often almost impalpable ; straight, divergent, and 

 frequently producing a second curved lamellar or granular 

 composition. Massive: composition columnar, or granular, 

 sometimes impalpable, often very distinct. The fracture of 

 impalpable compositions is uneven or even. 



1. Although the subspecies distinguished by the earlier writers on 

 mineralogy among the varieties of Blende, have been denominated after 

 their colors, yet they do not depend entirely or solely upon these colors. 

 Yellow Blende includes the more transparent varieties, whether of a 

 *reen, yellow or reddish-brown color. Brown Blende consists of the 

 more opake red and brown varieties. Black Blende is either black and 

 opake, or blood-red. Brown Blende has been further divided into folia- 

 ted, radiated and fibrous brown Blende : simple varieties and compound 

 ones, consisting of granular individuals, are contained in the first of these 

 divisions ; columnar compositions, in which the individuals are still dis- 

 cernible in the second ; and very thin .columnar or impalpable composi- 

 tions originating from them, which assume various imitative shapes, are 

 comprehended in the third division. The exact distinction of the above 

 varieties, requires much practice, and can be acquired only empirically ; 

 and even then many varieties will occur that render the distinction im- 

 possible, which is proof that the distinction itself is useless. 



2. When strongly heated in the oxidating flame of the blow-pipe, it 

 gives off vapors of zinc, which form a coating on the charcoal, but it does 

 not melt. It is soluble in nitric acid, during which process sulphuretted 

 hydrogen is evolved. 



3. Analysis. 



By THOMSOX. By GUENIVEAU. 



Zinc . . 59-09 . . 62-00 



Iron . . 12-05 . . 1.50 



Sulphur . 28-86 . . 34-00 



