SIUCATKS, TIT \\ATI ;>, l.h 465 



with the increase of iron and manganese in the formula they become 

 monoclinic. 



ZOISITE 



Zoisite. A basic orthosilicatc of calcium and aluminium; 

 Ca 2 Al 2 (A10H) (SiO ),; CaO = 24.6, A1 2 O 3 = 33.7, SiO 2 = 39.7, 

 NO = 2.0 ; Orthorhombic ; Type, Didigonal Equatorial ; & : b : c 



.1.196:1:. 3429; 100 A 110 = 31 47'; 001 A 101 = 28 58'; 

 001 A 011 = 18 56'; Common forms, a (100), b(010), m(110), 

 o(lll), d(101), f(011), r(120); Cleavage, b perfect; Brittle; 

 Fracture, uneven ; H. = 6-6.5 ; G. = 3.25-3.37 ; Color, gray, 

 white, or pale shades of green, pink, red, or yellow; Streak, white ; 

 Luster, vitreous to pearly; a = 1.696; p = 1.696; -y = 1.702; 

 y a = .006 ; Optically ( + ) ; Axial plane = 010 at times 001 ; 

 Bx. = A ; 2 V = 0-60. 



B.B. Fuses with intumescence at three to a white blebby slag, 

 gelatinizes after fusion. After strong ignition in the closed tube 

 yields water. 



General description. Crystals are prismatic in habit, elon- 

 gated parallel to the vertical axis, while epidote is elongated paral- 

 lel to the orthoaxis ; in the comparison of these two minerals the 

 c axis of zoisite is equivalent to the b axis of epidote. Deep stria- 

 tions on the prism zone parallel to the vertical axis are characteristic. 

 The crystals are rarely terminated, occurring in parallel or diver- 

 gent groups ; also massive. 



Thulite is a pink variety from Norway, and Traversella, in Pied- 

 mont ; the pink color is due to manganese. 



Zoisite contains but little iron and is essentially an aluminium 

 epidote. Clinozoisitc is a light-colored variety of epidote with 

 small amounts of iron ; the characteristic pistachio-green color of 

 epidote deepens with the increase of iron in the molecule. 



In rock sections zoisite appears in elongated crystals or granu- 

 lar; colorless, or pale; with the cleavage cracks parallel to the 

 macropinacoid distinctly developed. Relief is high, but the 

 interference color is a low first order gray. Extinction parallel. 

 The plane of the optic axis is usually parallel to the base, but at 

 times may be parallel to the macropinacoid. Optically ( + ). 



Zoisite is associated with the crystalline schists; rarely is it 

 found in granites or igneous rocks. As a secondary mineral it is 

 2n 



