CHARACTERISTIC. CLASS II. 



1. PRISMATIC. Hemi-prismatic. 



Cleavage, r + co, of a high degree of perfection. 



? = 40 52'. 



2 



H. = 7'5. 

 G. = 2-9 ... 3-2. 



Euclase. ii. 313. 



2. RHOMBOHEDRAL. Di-rhombohedral. P = 151 9', 59 47'- 



Cleavage, R eo. Less distinct, P + co. 

 H. = 7'5 ... 8-0. 

 G. = 2-6 ... 2-8. 



Emerald. ii. 316. 



VI. QCARTZ. Rhombohedral, prismatic. 

 Cleavage, not axotomous. 

 H. = 5-5 ... 7-5. 

 G. = 19 ...'2-7. 



1. PRISMATIC. Prismatic. 



Cleavage, P + co = 120 (nearly). r 4- co. 

 Dichroism, parallel and perpendicular to the axis. 

 H. = 7-0 ... 7-5. 

 G. = 2-5 ... 2-6. 



Cordierite. ii. 319. 



2. RHOMBOHEDRAL. Rhombohedral. R = 75 55'. 



Combinations, hemi-rhombohedral and hemi-di-rhom- 

 bohedral ; R + n and (P + n') m with inclined faces, 



P + n" with parallel faces. = 94 15'. 



Cleavage, P = 133 44', 103 35'. Commonly 



somewhat less distinct. P + co. 

 H. = 7*0. 

 G. = 2-5 ... 2-7- 



Quartz. ii. 321. 



3. UNCLE AV ABLE. Reniform ... massive. 



Cleavage, none. 



