472 MINERALOGY 



ster, New York, associated with serpentine. Chondrodite occurs 

 at Sparta, New Jersey, and at Amity and Warwick, New York, 

 in a limestone associated with spinel. 



By hydration they alter to serpentine and sometimes to brucite. 



ILVAITE 



Ilvaite. CaFe 2 (FeOH)(SiO 4 ) 2 ; CaO = 13.7 ; FeO = 35.2 ; 

 Fe 2 O 3 = 19.6 ; Si0 2 = 29.3_; H 2 O = 2.2 ; Orthorhombic ; Type, 

 Didigonal Equatorial ; & : b : c = .6665 : 1 : .4427 : 100 A 110 = 33 

 41'; 001 A 101 - 33 35'; 001 A 011 = 23 53'; Common forms, 

 b (010), m (110), s (120), o (111) ; Cleavage, b and c distance a 

 and m less so ; Brittle ; Fracture, uneven ; H. = 5.5-6 ; G. = 3.99- 

 4.05 ; Color, iron-black ; Streak, black to brownish ; Luster, sub- 

 metallic; Opaque. 



B.B. Fuses easily with some intumescence to a slag which 13 

 magnetic ; gelatinizes with HC1. Manganese may replace some 

 of the iron, when it will yield reactions for that metal. 



General description. Crystals are prismatic in habit, with 

 striations on the prism zone parallel to the vertical axis. It is 

 not a common mineral ; it occurs on the isle of Elba in a dolomite, 

 and takes its name from the Latin term for the island. It has also 

 been reported as from Somerville, Massachusetts, and Cumberland, 

 Rhode Island. 



The crystals are not unusually coated with a yellow or brown 

 oxide of iron, which is the result of oxidation. 



CALAMINE 



Calamine. Hemimorphite ; Hydrous orthosilicate of zinc ; 

 Zn 2 Si0 4 .H 2 ; ZnO = 67.5 ; Si0 2 = 25.0 ; _H 2 = 7.5 ; Ortho- 

 rhombic ; Type, Didigonal Polar ; a : b : c = .7834 : 1 : .4778 ; 

 100 A 110 = 38 4'; 001 A 101 = 31 23'; 001 A 011 =25 32'; Com- 

 mon forms, b(010), c(001), m(110), i(031), v(121), t (301) ; 

 Twinning plane 001, supplementary twins; Cleavage, prismatic 

 perfect ; Brittle ; Fracture, uneven ; H. = 4.5-5 ; G. = 3.40-3.50 ; 

 Color, white, brown, or yellow; Streak, white; Luster, vitreous 

 to adamantine; Transparent to translucent; Pyroelectric ; 

 a = 1.613; p = 1.617; 7 = 1.636; y - a = .023 ; Optically 

 ( + ) ; Axial plane 100; Bx a = c; 2E = 78 39'; 2V = 46 9'. 



