the Native Red Iron- Vitriol of Fahlun. 49 



The regular forms of botryogene belong to the hemipris- 

 matic system of Mohs. The usual crystalline forms of it are 

 represented in Plate II., Figs. 1 and 2. Fig. 3 is the projec- 

 tion of the latter upon a plane parallel to the base, and viewed 

 in the direction of the axis; in which figure the parallelism 

 of the edges of combination is more easily seen than in the per- 

 spective view of it in Fig. 2 itself. From the admeasurement 

 of the edges, between P and q, P and g, and between g and g, 

 I obtained the following angles : — Inclination of 

 n on n = 125° 22' P on g = 113° 37' fonf- 81° 44' 

 <7ong = 141° 0' g on g =119° 56' yon P=zl25°3V 

 The pyramid Fig. 4 may be considered as the fundamental 

 form of the series of crystallization, to which the combinations 

 Figs. 1 and 2 belong. In this pyramid the lines a:b : c: d are 

 in the proportion of 1.98 : 3.62 : 5.59 : 1. The secondary faces 

 occurring in nature, expressed by the crystallographic signs of 



Mohs, are : P — x for P, -— - for n 9 — li^_±i for>, Pr— 1 



for q, P -j- oo for g, (Pr -f- 00 ) 5 for/, and Pr -f- oo for u. 



The form of the crystals is in general pretty distinct ; yet 

 they were too imperfectly formed in the specimens I examin- 

 ed to permit any thing more than an approximation to the real 

 angles within ten minutes of a degree. They are not above 

 two lines in length ; and the faces of the prisms f and g are 

 striated parallel to the axis. The inclined faces are more per- 

 fectly formed. 



Cleavage takes place with considerable facility parallel to the 

 faces g. There are traces also parallel to f. 



The lustre of botryogene is vitreous. It is translucent. Its 

 colour is a deep hyacinth-red, which, however, in compound 

 and massive varieties, passes into ochre-yellow, which is like- 

 wise the colour of its streak. 



It is sectile, and becomes a little shining in the streak. The 

 hardness is = 2.25... 2.5, a little inferior to alum. The speci- 

 fic gravity I found == 2.039. It is but slowly soluble in wa- 

 ter, and does not therefore possess so powerful an astringent 

 taste as the common vitriol of iron. 



The crystals of this substance are usually aggregated in re- 

 niform and botryoidal shapes, consisting of globules with a 

 crystalline surface. A small specimen about half the size of 



VOL. IX. NO. I. JULY 1828. D * 



