Foreign Notices in Mineralogy, &c. 31 
fr peo joints parallel to more than four of the planes of 
the wm, I consider the right rhombic prism as 
oe primary form. "The angles of this prism are 95° and 
; the planes which give the angle of 95° appear on ma- 
a eo the crystals as a dihedral termination to secondary 
forms, analogous to some prismatic varieties of sulphate of 
barytes. The crystals are generally very minute, and ap- 
r sometimes in small bunches, radiating from their com- 
mon point of attachment to the matrix. 
Besides the cleavages parallel to its planes, the rhombic 
prism divides also in the direction of its et diagonal, 
and its height is to the edge of the base as 2 to 
_ The fact that peesenee itself to our notice shee of so dis- 
a difference of rystalline Soch by ach 
ay, ' ri lL end fir m the in mat sats a hat - 
between the eee sant cryitallograpbieat & aracters of 
minerals; and it appears to disprove M. Beudantyr Cane 
ture, that only the secondary form of crystals are affected 
by a change in the proportions of their constituent chemi- 
cal elements. 
li is remarkable, too, that lead should. alone present so 
paar 
many instances of a es Eee: at thes same time 
with two acids. — Sites area 
London, 13th May, 1820, 
a No. 6 of Edinburgh hsaseeed janis eo 
“New works on Petrifactions.—1. The well inti ge- 
, Baron Von Schlotheim, is just about to publish : an 
extensive work on petrifactions, or j from the ac- 
curacy, and extensive aaa oie aut a it cannot 
also —— a mated on ae me 
own coal, and other cers 9am ef thes ie’ ere 
nfl aiggalet has 6 Sah us? ae a Leip od : 
fi ork; eat 
| the 
