301 PHYSIOGBArHT. CI.ASS u. 



editing fine works in other hard stones. Emery yields a 

 well known grinding material. 



4. PRISMATIC CORUNDUM. 



Prismatic Corundum or Crysoberyl. JAM. Syst. Vol. I. 

 p. 64. Man. p. 180. Chrysoberyl. PHILL. p. 89. 

 Krisoberil. WERN. Hoffm. H. 15. I. S. 424. Chryso- 

 beryll. HAUSM. II. S. 385. Chrysoberyll. LEONH. S. 

 437. Cymophane. "HAUY. Traite', T. II. p. 491. 

 Tabl. comp. p. 30. Traite^, 2de Ed. T. II. p. 303. 



Fundamental form. Scalene four-sided pyramid. 

 I 1 = 139 53', 86 16', 107 29'. Vol. I. Fig. 9. 

 R. G. 



a i b : c = 1 : V 2-9731 : J 0-6567. 



Simple forms. P (o) ; P + QD = 128 35'; (P) 3 

 (n) ; (P + oo)* CO = 70 41' ; (Pr + oo)' (*) 

 = 93 33' ; ?r (i) - 119 46' ; ?r + oo (T) ; 

 Pr -f OD (M). 



Char, of Comb. Prismatic. 



Combinations. l.?r. Pr-f oo. Pr+ QD. Haddam, 

 Connecticut. 



2. Pr. (Pr+oc) 3 . Pr-f- oo. Pr+ oo. Haddam. 



3. Pr. P. (f + Go) 3 . Pr+ a. Pr-f- GD. Fig.25. 

 Siberia. 



4. ?r. P. (?)*. (P-foo) 3 . Pr-f oo. Pr+ oo. 

 Brazil. 



Irregular forms, grains, pebbles. 



Cleavage, Pr -f co and Pr -f- oo, not very distinct, 

 the first a little more easily obtained. Faint 

 traces parallel to P QD. Fracture conchoidal. 

 Surface, the vertical planes, and particularly 

 Pr -|- oo, striated parallel to their common edges 



