Determination of Diallage. 131 



ing kinds, viz. 1st, The real Smaragdite, of a grass-green colour ; 

 2d, The less distinct varieties of the same, as common; and, 3d, The 

 diatomous Schiller-spar from the Hartz, as falcons Diallage ; part 

 of the latter forms probably also the 4tth kind, or Schiller-stein. 

 HAUSMANN endeavours to explain the single or monotomous 

 cleavage of the different species of Schiller-spar, and the splen- 

 dent laminae of Diallage, as produced out of the two faces that 

 occur in Hornblende, by supposing one of them to become more 

 perfect at the expence of the other, whereby, in most cases also, 

 " the angle of inclination is changed, and approaches more or 

 " less to a right angle." A supposition of that kind, if granted, 

 would be sufficient to overthrow the whole of crystallography, 

 and that which has just now been quoted, has, for this reason, 

 been very strongly objected to by HAUY*. The substances 

 and formations, in fact, of HAUSMANN'S system, do not aUow 

 of any strict comparison with either genus and species, or with 

 species and subspecies ; hence it will be impossible to assert, whe- 

 ther or not HAUSMANN means to comprehend Smaragdite un- 

 der the species of Hornblende. 



This latter opinion, very often quoted, indeed, but more com- 

 monly with the view of refuting it, seems in general to have 

 gradually disappeared ; and the most recent systematical mine- 

 ralogists agree in considering the perfectly foliated green varie- 

 ties of the Smaragdite of SAUSSURE as a particular species, which 

 they place accordingly in their systems. Yet among the vast 

 number of works that more especially treat of the present sub- 

 ject, there is none which does not attempt to reproach the rest 

 with the uncertainty of their determinations, and the want of 

 distinctness in their descriptions, though its own assertions can 



* Journal des Mines, xxxviu. p. 161. 

 R 2 



