of Crystallized Bodies. 91 



position take place parallel to all the faces of R — 1. Very 

 often the substance of the two or more individuals may be 

 separated with considerable facility in the faces of composi- 

 tion, and produces what has hitherto very often been erron- 

 eously considered as cleavage. Thin plates of one individual 

 engaged in another, according to this law, occur from the most 

 beautifully transparent Iceland varieties, down to the quite 

 opaque ones ; they also occur in other species, whose forms re- 

 semble those of Calcareous spar, as in the Paratomous Lime- 

 haloide, mentioned above, but particularly in Sparry Iron-ore. 

 I have succeeded in extracting from a variety of the latter, 

 found at Niederalpel in Stiria, the form represented in Fig. 



20, bounded partly by faces of cleavage P, P, P, partly by 

 faces of composition g, g, g, the whole being, in no small 

 degree, alike to certain varieties of Sphene. Also, in respect 

 to cleavage, the composition perpendicular to the terminal 

 edges of R sometimes takes place at the same time in three di- 

 rections, as in the case of Fig. 17. Thus, is the variety Fig. 



21. composed of four individuals, three of which are joined 

 to a central one, according to the above-mentioned law. 

 Many specimens of this kind, containing even a greater num- 

 ber of individuals, joined to the outer ones of the composi- 

 tion, occur in a limestone quarry near Harzgerode. 



The preceding law of regular composition is so frequently 

 found in Red Silver-ore, that it may be considered as one of 

 the greatest rarities to observe a group of crystals of this 

 substance, which does not present it. The simplest modes 

 of this composition are represented in Fig. 22. where it takes 

 place only on one of the terminal edges of R — 1, and Fig. 

 23. where it is met with on all the three edges at once. The 

 sign of Fig. 22. is R — 1 . P + oo, {?—!-•?—}] ; the sign of 



Fig. 23. R — 1 • P + oo, [R-s.R-ij. But generally each 

 of the three individuals, joined to the central one, in the 

 edges a, a, a, has two other individuals attached to the remain- 

 ing edges b, b, and b, so that the group becomes composed of 

 ten individuals, or even of more if to these again other indi- 

 viduals are fixed. Large crystals are often surrounded in 

 this manner by smaller ones, branching out, as it were, from 

 the main shaft, on the alternating edges of the six-sided 

 prism. There are hollow six-sided prisms of Red Silver-ore, 

 from the mine of Kurprinz, in the possession of Dr. Ro- 



