ORDER VII. PRISMATIC QUARTZ. 319 



titles in drusy cavities of primitive rocks in various places 

 of Salzburg; in Elba ; at Haddam in Connecticut, and other 

 localities of America, &c. 



5. Rhombohedral Emerald, when clear and transparent, 

 is employed as an ornamental stone, and is highly valued 

 if it is free from flaws, and possesses a fine emerald-green 

 colour, and a certain size. Beryl is of much less value. 



GENUS VI. QUARTZ. 

 1. PRISMATIC QUARTZ. 



lolite. JAM. Syst. Vol. I. p. 172. Prismato Ilhomboi- 

 dal Quartz or lolite. Man. p. 193. lolite. Dichro- 

 ite. PHILL. p. 93. lolite. Peliom. WERN. Hoflm. 

 H. B. I. S. 589. IV. 2. S. 11?. Dichroit. HAUSM. II. 

 S. 659. Cordierit. LEONH. S. 420. lolithe. HAUY. 

 Tabl. comp. p. 61. Cordierite. Traite', 2de Ed. T. 

 III. p. 1. 

 COEDIER. Journ. des Mines. T. XXV. p. 129. 



Fundamental form. Scalene four-sided pyramid 



of unknown dimensions. Vol. I. Fig. 9. 

 Simple forms. P QD; P; P + QD = 120 



(nearly) ; Pr + 1 ; ?r + oo ; Pr + oo. 

 Char, of Comb. Prismatic. 

 Combinations. 1. P oo. P + oo. Pr -f- x. Cabo 



de Gata. 2. P oo. P. Pr + 1. P + oo. 



(?4-oo) 5 . Pr + oo. Pr + oo. Ujordlersoak, 



Greenland. 

 Cleavage, P + oo and ?r -f- oo indistinct. Fracture 



conchoidal. Surface of some crystals rough and 



dull. 

 Lustre vitreous. Colour various shades of blue, 



generally inclining to black. Streak while. 



Transparent . . . translucent ; blue if viewed in 



