466 MINERALOGY 



derived from the alteration of the plagioclases. Saussurite is a 

 mixture of plagioclase and zoisite in various proportions. 



It occurs in various localities in Massachusetts, Connecticut, 

 and North Carolina ; at Ducktown, Tennessee ; and in the Coast 

 Range, California. The synthesis of zoisite is uncertain, as the 

 products of various fusions have contained no water. 



Epidote. A basic orthosilicate of calcium aluminium and iron, 

 Ca 2 (AlFe) 2 (AlOH)(SiO 4 )3; CaO = 23.73, A1 2 O 3 = 25.95, Fe 2 O 3 

 = 10.18 (when Fe : Al : : 4 : 1), SiO 2 = 35.20, H 2 O = 1.91 ; Mono- 

 clinic ; Type, Digonal Equatorial ; a : b : c = 1.5787 : 1 : 1.8036 ; 

 p = 64 37' = 100 A 001 ; 100 A 110 = 55; 001 A 101 = 34 43'; 

 001 A 011 =58 28'; Common forms, c (001), a (100), m(110), 

 e(101), r(101), o(011), d(lll); Twinning plane, 100 contact 

 twins, also 001, but rare ; Cleavage, basal perfect and a imperfect ; 

 Brittle ; Fracture, uneven ; H. = 6-7 ; G. = 3.25-3.5 ; Color, 

 shades of green, also yellow, red, or gray ; Streak, white ; Luster, 

 vitreous; Transparent to opaque; a = 1.724; p = 1.729; \ 

 = 1.734; -y - a = .010; Optically ( - ); Axial plane = 010; 

 Bxa A c 2-3 in the acute angle P; 2V = 73-88. 



B.B. Fuses at three with intumescence to a black blebby glass, 

 which when powdered is generally magnetic and gelatinizes with 

 HC1. After strong ignition in the closed tube yields water. 





FIG. 493. Epidote, Sulzbachthal, Tyrol. The Central Figure is from Prince-of- 

 Wales Island, Alaska. 



General description. Crystals are elongated parallel to the 

 orthoaxis, with terminations generally rich in faces ; often twinned 



