298 



DESCRIPTIVE MINERALOGY. 



HORNBLENDE. 



Amphibole. Hauy and Thomson, — Hornblende. Phillips, She-par A and Dana. Hemiprismatic Augite. Jameson. — 



Hemiprismatischer Augit-Spath. Mohs. 



Cleaveland includes under Hornblende only the dark-coloured varieties. He lias Tremolite as a distinct species, and 

 Actynolite as a subspecies under Hornblende. Beudant has a subgenus Amphibole, and under it he places Tremolite 

 and Actinote as species. Phillips includes under the general name Hornblende, Common Hornblende, Pargasite, Tre- 

 moUte, Pyraliolite, ActynoUte, and Asbestus. As it is exceedingly difficult to draw the line between these varieties, I 

 shall follow this author. 



Fig. 223 (*«: 



Description. Colour green, white, black, grey, blue and brown. It occurs regularly crys- 

 tallized ; also in lamellar and fibrous masses. Primary form an oblique 

 rhombic prism. Fig. 223 {his). M on M' 124° 30' ; M or M' on P 103° 

 1'. Cleavage parallel with M highly perfect ; less distinct parallel with 

 P, and with the diagonals of the prism. Fracture conchoidal, uneven 

 and slaty. Lustre vitreous, vitreo-pearly, pearly and vitreo-resinous. 

 Ranges from transparent to opaque. Hardness from 5 to 6. Specific 

 gravity from 2.90 to 3.35. Fusible before the blowpipe, with more 

 or less ease, into a white translucent or opaque glass, or into one that 

 is green or black, depending upon the variety. It is not easily attacked 

 by acids. . 



Hornblende is distinguished from diallage and hypersthene chiefly by its cleavage. Diallage 

 has only one distinct cleavage ; hypersthene three, of which two are silvery, and one copper- 

 like ; while hornblende has only two, and moreover by transmitted light displays a deep red 

 colour. It is more difficult to distinguish hornblende from pyroxene. Prof. G. Rose has in- 

 deed proposed to unite them, and he has presented a great number of facts in favour of their 

 identity.* 



Varieties. Hornblende — Carinthin. This includes all those varieties with dark green 

 and black colours, whether crystallized or massive. The lustre varies from pearly to pearly- 

 vitreous. It is usually opaque, and before the blowpipe, fuses into a black brilliant glass. 

 The term basaltic has been particularly applied to those cleavable and highly crystalline black 

 hornblendes which occur in basaltic and amygdaloidal rocks. 



Pargasite. A name originally given to a hornblende from Pargas in Finland. It is somewhat 

 translucent, and is usually of a bottle-green colour. In other respects, it agrees with the 

 preceding variety. 



Actynolite and Calamite. These are light green, greenish grey, and sometimes brown and 

 yellow. They are seldom crystallized, (and then generally in reed-like crystals ;) more fre- 



AllarCs Manual of Mineralogy, 149. 



