Determination of Diullage. 145 



1 could get no information respecting their locality ; but there 

 exists a variety of the same species in roughly terminated im- 

 bedded crystals in the Weiss-stein of Chursdorf, near Penig in 

 Saxony, where they occur in small irregular veins, composed of 

 Felspar, Quartz and Tourmaline. The crystals of Serpentine are 

 not pseudomorphous ; for, besides the peculiarity of their series 

 of crystallisation, they present very distinctly, faces of cleavage in 

 the direction of the prism (Pr + <x) 3 = 82 27', and of Pr+ oo, 

 its greater diagonal, exactly agreeing with their external form. 

 The imbedded crystals, too, distinctly exhibit these faces of clea- 

 vage, even if the external form should be entirely obliterated by 

 their contact with other minerals. 



Yet an exact knowledge of the forms was not required ; and 

 even without it, the specific gravity, if properly attended to, 

 would have been an argument not to be refuted, against the opi- 

 nion that Serpentine is identical with a mixture of Gabbro and 

 Talc. The component parts of Gabbro are the following species : 



Saussurite, the specific gravity of which is - above 3.2 



Hemiprismatic Augite-spar, . . above 2.9 



Paratomous Augite-spar, . . above 3.2 



Labrador, a bo ve 2 g 9 



Tal c> above 2.7 . 



Now, the specific gravity of Serpentine being 2.507, in the 

 above-mentioned crystallised variety, and = 2.488 in the clea- 

 vable one from Saxony ; it appears not only below a mean term 

 of all the specific gravities of the above-mentioned minerals, but 

 far less than the lowest limit of any one of those species taken 

 separately, which are said to produce the mixture. 



Yet there exist some varieties of Serpentine, which, to a some- 

 what higher degree of specific gravity, join distinct traces of a 

 crystalline formation. Thus the variety from Monteferrato gives 

 2.716 ; it contains no magnetic (octahedral) Iron-ore, as it does 

 not affect the magnetic needle, which is the case with other va- 



VOL. X. P. I. T 



