Determination of Diallage. 137 



often cracked in other directions than those of the less distinct 

 faces of cleavage, the latter of which correspond to P r + oo of 

 hemiprismatic Augite-spar, and that they shew a tendency of sepa- 

 rating into rhombs, a property owing to the real faces of the clea- 

 vage of paratomous Augite-spar, which is spread in thin laminae 

 throughout the mass of the hemiprismatic. As long as it is 

 within the powers of our senses to distinguish, and to separate 

 these heterogeneous substances, the application of the Character- 

 istic will clearly lead to their respective species ; and no doubt in 

 regard to their determination can ever remain, as long as their 

 natural-historical properties can be ascertained with a sufficient 

 degree of exactness. 



Professor MOHS, very long ago, and even during his residence at 

 Gratz, in consequence of accurate investigations, had recognised 

 the granular varieties from the Saualpe and the Bacher, as belong- 

 ing to paratomous, the latter also in part to hemiprismatic Augite- 

 spar, and united them accordingly with these species. The only 

 varieties still doubtful were those from other countries, so very 

 much distinguished by the perfection and high pearly lustre of 

 their laminae. The establishment of Smaragdite into the species 

 of axotomous Schiller-spar in the Characteristic of MOHS, was al- 

 most entirely founded upon foreign authority. It disappears 

 now from the series of particular mineral species, all its varieties 

 having been referred to those of hemiprismatic and paratomous 

 Augite-spar, in the properties of which they partake. 



Although whatever belongs to the determination of the spe- 

 cies has thus been completed, and therefore the more peculiar 

 object of this paper attained ; yet I shall conform to the usage 

 hitherto received in mineralogy, not to pass over entirely the 

 instruction derived from other sciences foreign to natural his- 

 tory, in respect to the species under consideration, and shall 

 therefore give a brief account of the chemical constitution of 



VOL. x. p. i. s 



