Mr. Brooke on Cupreous Sulphate of Lead. 267 



planes, from which it is evident that the primary form is an 

 oblique rhombic prism, and from the angles given below it 

 approaches very nearly, if it be not the same as that of 

 euclase. It has also a bright cleavage through the oblique 

 diagonal, similar to that of euclase, and no very distinct 

 cleavage in any other direction. 



The annexed figure exhibits the form of the crystal I have 

 alluded to, the terminal planes of which are, however, too 

 imperfect to afford accurate measurements. 



= 107° 20' 

 = 121 30 



The perfect identity of the forms of Zoizite and Euclase 

 depends obviously on the relative dimensions of the primary 

 forms, as well as upon the angles of the prisms ; and as those 

 dimensions can be deduced only from accurate measurements 

 of the terminal planes, it is to be hoped that those who possess 

 better crystals will supply the deficient angles, and complete 

 the description of the form. 



Cupreous Sulphate of Lead. 



A specimen 1 have lately obtained of this substance has 

 enabled me to give the annexed figure and measurements of 

 the crystals. The primary form is an oblique rhombic prisma 

 a terminal edge of which is to a lateral edge as 19 to 8 very 

 nearly, the plane angles of the terminal plane at the extre- 

 mities of the oblique diagonal being 59° 12'. 



Planes cl. 



c2, 



T 



A, 



c3, 



A, 



c4, 



1 



A, 



c5, 



i 

 A, 



1 

 H. 



Symbols.... A, 

 P,M = 96° 25' 

 P,A = 102 45 

 P,cl = 176 35 

 P,c2 = 161 30 

 P,c3 = 156 10 

 P,c4 = 151 40 

 P,c5 = 129 40 

 M,M'= 61 



• Corresponding; planes of euclase, as measured by W. P. (See liis 

 ^ ' 2 M 2 Ilemitrope 



