SII.ICATKS, T1TANATI S. KT< 



44'J 



ami lirurite may appear as alteration products. Chromite is 

 :;lmost always associated with the alteration of peridotite or \\ith 

 tin -. i p. nt in. n >ulting from it, as at the Maryland locality. 



Fio. 487. Section of Olivine, showing the Cracks filled with Secondary Mag- 

 netite and a Marginal Band of Enstatite and Hornblende. 



Some nickel deposits, as the garnierite of New Caledonia, are asso- 

 ciated with olivine or its alteration products, as also platinum and 

 the diamonds of South Africa. 



Artificially the olivine group is easily synthesized by a direct 

 fusion of their constituents in the right proportion, particularly 

 if a little boric acid is added to lower the fusing point. They are 

 therefore common products of slags and are also found in meteors. 

 When olivine is fused with a little silica in excess, enstatite is 

 formed; if the silica is increased, then pyroxenes are formed. 



MONTICELLITE 



Monticellite. Calcium magnesium orthosilicate, CaMgSi0 4 ; 



CaO = 35.9, MgO = 25.6^ SiO 2 = 38.5 ; Orthorhombic ; Type, 



Didigonal Equatorial ; a : b : 6 = .4337 ; 1 : .5758 ; 100 A 110 = 23 



27'; 001 A 101 = 53; 001 A Oil = 29 56'; Common forms, as 



in olivine ; Cleavage, b distinct ; Brittle ; Fracture, conchoidal ; 



H. = 5-5.5 ; G. = 3.03-3.25 ; Color, white, gray ; Streak, white ; 



Luster, vitreous; Transparent to translucent; a = 1.650; P 



l.(i()2; y = 1.668 -y - a = .018; Optically (-); Axial plane 



001 ; Bx a = b ; 2 V = 37. 



2o 



