516 MINERALOGY 



soda and dissolved in HNO 3 yields a yellow precipitate with ammo- 

 nium molybdate (P 2 O5) . Becomes blue when treated with cobalt 

 solution (Al) . Insoluble in acids. 



General description. Crystals are plus and minus unit pyra- 

 mids, or combinations of these with the unit orthodome; other 

 forms are rare. More often massive or granular, and associated 

 with quartz and cyanite in slates. At Crowder Mountain, Gaston 

 County, North Carolina, it is associated with corundum ; at Graves 

 Mountain, Georgia, it occurs in fine sky-blue crystals, an inch or 

 more in length, associated with rutile and cyanite. Crystals six 

 inches long occur in pockets of quartzite in Wermland, Sweden. 



VIVIANITE 



Vivianite. Fe 3 (PO 4 ) 2 . 8 H 2 ; Hydrous ferrous phosphate ; 

 FeO = 43.0, P 2 5 = 28.3, H 2 O = 28.7 ; Monoclinic ; Type, 

 Digonal Equatorial ; a : b : c = .7498 : 1 : .7016 ; P = 75 34' = 

 001*100; 100 A 110 = 35 59'; 001 A 101 =49 46'; 00^011=34 

 11' ; Common forms, a (100), b (010), m (111), n (101) ; Cleavage, 

 clinopinacoidal perfect, almost micaceous, very thin laminae 

 slightly flexible and sectile ; H. = 1.5-2; G. = 1.58-2.68; Color, 

 blue to green; Streak, white to blue, darkens on exposure; 

 Luster, vitreous to pearly ; Transparent to opaque. 



FIG. 517. Vivianite. Leadville, Colorado. The smaller specimen is from Red 



Bank, N.J. 



