512 MINERALOGY 



characteristic of the zone of oxidation and is therefore found in 

 the superficial workings of lead mines. While it is a valuable ore of 

 lead, it occurs only in small quantities. 



Good specimens have been obtained at the Wheatley mine, 

 Chester County, Pennsylvania. It occurs in small quantities at 

 various localities in New England and North Carolina. 



Mimetite, Pb 5 Cl(As0 4 )3, a chlorarsenate of lead, is very similar 

 in habit and occurrence to pyromorphite, with which it is iso- 

 morphous. In color it is yellow to greenish white and often in 

 globular or barrel-shared crystals. 



Vanadinite, Pb 5 Cl(FO 4 ) 3 , a chlorvanadate of lead, another 

 member of the apatite group, in which V 2 O 5 takes the place of P 2 O 5 

 or As 2 Os. It is similar in habit and crystallization, but usually red 

 to light yellow in color. It is associated with lead ores at various 

 localities in Arizona and New Mexico. 



Endlichite is a light yellow variety containing arsenic, occurring 

 in Sierra County, New Mexico. 



AMBLYGONITE 



Amblygonite. Li(AlF)PO 4 ; Li 2 O = 10.1, A1 2 3 = 34.4, P 2 O 6 

 = 47.9, F = 12.9 ; Triclinic ; Type, Centrosymmetric ; : b : c = 

 .7334:1: .7633; a = 108 51'; = 97 48'; <y = 10627'; 100 A 010 = 

 69 25'; 100 A 001 = 75 30'; 010 A 001 = 67 38'; 100 A 110 = 29 

 35' ; 001 A 021 _= 74 40' ; Common forms, c (001), a (100), m (110), 

 M(ll0), e(021); Twinning plane, 101 and 101, polysynthetic 

 twins common, the two sets of striations making an angle of 89 8' ; 

 Cleavage, basal perfect, at times e also; Brittle; Fracture, un- 

 even ; H. = 6 ; G. = 3.01-3.09 ; Color, white, gray, or pale blue, 

 green, and brown ; Streak, white ; Luster, vitreous ; Translucent 

 to opaque; a = 1.579; p = 1.593; -y = 1.597; y- a = .018; 

 Optically (-). 



B.B. Fuses easily at 2 with intumescence and yields a lithium 

 flame, especially when fused with the fluorite flux. When fused 

 with soda and dissolved in nitric acid, shows phosphoric acid with 

 ammonium molybdate. Usually contains some water from the 

 replacement of F by OH. 



General description. Crystals are coarse and not well formed, 

 usually in cleavable masses. It occurs in the coarse granites and 



