456 



MINERALOGY 



Zonal structure and optical anomalies are not uncommon. 

 Vesuvianite is a mineral produced by contact metamorphism. 



It appears in schists but more often in granular limestones, where 



it is associated with 

 garnets, epidote,wer- 

 nerite, wollastonite, 

 and diopside. It is 

 a common mineral 

 in the ejected blocks 

 of limestone on 

 Monte Somma, Ve- 

 suvius ; in small bril- 

 liant crystals also in 

 the Ala thai, Pied- 

 mont. Clear green 

 brilliant crystals oc- 

 cur at Amity, New 

 York. It occurs at 

 Rumford and Po- 

 land, Maine, in lime- 

 stones associated 

 with garnets; at 

 Newton, New Jersey, 

 with corundum and 

 spinel. 

 The clear crystals are sometimes polished, but it makes an 



indifferent gem known as idocrase. 



It is seldom found altered, though pseudomorphs after vesuvian- 



ite are known. 



Vesuvianite has not been produced artifically; when fused it 



breaks down and on cooling the melt produces olivine, anorthite, 



and melilite. 



FIG. 489. Vesuvianite, Poland, Maine. The Upper 

 Crystal is Viluite from Siberia. 



ZIRCON 



Zircon. Zirconium orthosilicate, ZrSi0 4 ; ZrQ >r = 67.2 ; Si0 2 

 = 32.8 ; Tetragonal ; Type, Ditetragonal Equatorial ; c = .6403 ; 

 001 A 101 = 32 38'; 110*111=47 50'; 111 A ill =56 40'; 

 Common forms, p(lll), m(110), u (331), x (311) ; Twinning 

 plane 111, geniculate twins; Cleavage, m distinct, p less so; 

 Brittle ; Fracture, conchoidal ; H. = 7.5 ; G. = 4.68-4.7 ; Color, 



