98 NEW YORK STATE MUSEUM 



Hauynite Na 2 Ca(NaSo 4 .Al)Al 2 (Si0 4 ) 3 



Hauynite is a sodium, calcium and aluminium orthosilicate 

 with some sodium sulfate, 



Hauynite occurs in glassy rounded isometric crystals and 

 grains of a blue to green color in igneous rocks and lavas. 



Lazurite (lapis lazuli) Na 4 (NaS 3 .Al)Al 2 (Si0 4 ) 3 



Lazurite is an orthosilicate of sodium and aluminium with 

 sodium sulM. 



It occurs in deep blue masses and rarely in isometric crystals. 

 Lazurite was formerly used as a natural pigment, producing the 

 deep blue color known as ultramarine; it has now been almost 

 entirely superseded by the artificial product of that name. 



Garnet R n s B ra 2 (SiOJ a 



Garnet is an orthosilicate of the general formula R II 3 R III 2 

 (Si0 4 ) 3 in which R n may be calcium, magnesium, ferrous iron, 

 or manganese and R 111 aluminium, ferric iron or chromium, rarely 

 titanium. The varying proportions of these elements give rise 

 to numerous varieties, the principal types of which will be dis- 

 cussed under " Varieties." 



Garnet crystallizes in the normal group of the isometric sys- 

 tem. Fig. 216-18 show the common types of crystals. It occurs 



Fig. 216 Fig. 217 Fig. 218 



in isolated, embedded crystals, in drusy incrustations and in 

 granular, lamellar and compact masses, also as rounded grains 

 and in sand. 



The luster is vitreous to resinous and the color commonly 

 brown, red or black but also yellow, pink, white, green and 

 violet. In hardness garnet ranks between quartz and corundum. 



