Determination of Diallage. 139 



has adopted HAUY'S opinion, that Green Diallage is different from 

 either Hornblende or Augite, and that it constitutes but one and 

 the same species with Diallage metalloids ; and, in many instan- 

 ces, even the determination of the rocks is founded upon this 

 supposition. 



The mineral most commonly accompanying green Diallage, is 

 Saussurite or Jade, a species considered as a variety of compact 

 Felspar, by both WERNER * and HAUY f , although it had long 

 before been pointed out as a particular species, and acknowledged 

 as such by a great number of mineralogists. HAUY takes for 

 granted that the forms are identical, but even these deviate in 

 Saussurite from the forms of the different species of Felspar : for 

 it is possible to obtain its forms of cleavage, out of certain granu- 

 lar varieties, in the shape of oblique-angular four-sided prisms, 

 of nearly 124 and 56, which can very easily be cleaved, parallel 

 to their faces, and with a less degree of distinctness, also paral- 

 lel to their short diagonal. The difference between the specific 

 gravity of Saussurite, and that of the Felspars, is as remarkable, 

 and still more easy to be ascertained; the limits of the former be- 

 ing 3.2 and 3.4, whereas the latter never exceeds 2.8. The spe- 

 cific gravity of a compact Saussurite from Corsica, I found =3.206; 

 that of two specimens of the granular variety, one from Piedmont, 

 and another from Bayreuth, 3.253 ; of a compact one from 

 the shores of the Lake of Geneva, =. 3.343. The hardness of 

 Saussurite, is by many authors said to be superior to that of 

 rhombohedral Quartz ; yet it is no higher than 5.5 of the scale 

 of MOHS, (between Apatite and Felspar), if taken with the neces- 

 sary precautions by the assistance of a file. On account of its 

 remarkable toughness, it nevertheless very often scratches rhom- 



* HOFFMANN'S Handbuch, Th. ii. a. s. 339- 

 t Traite, 2de Ed. T. iii. p. 95. 



S 2 



