100 NEW YORK STATE MUSEUM 



As a rock constituent chrysolite occurs in the rocks of the 

 Cortlandt series in the vicinity of Peekskill, Westchester co. and 

 Stony Point, Rockland co. N. Y. 



Transparent varieties of olivin are cut as gems and are 

 known to jewelers as olivins or peridots. 



Willemite Zn.SiO, 



Willemite is an orthosilicate of zinc containing 72.9^ zinc oxid 

 and 27.1$ silica. A considerable part of the zinc is replaced by 

 manganese in the variety troostite. 



Willemite occurs in hexagonal crystals of the trirhombohedral 

 class prismatic in habit. It is more commonly found in granular 

 masses and disseminated grains. The luster is resinous and the 

 color greenish yellow to apple-green when pure but flesh-red in 

 the manganese bearing variety. 



Willemite is chiefly found associated with franklinite and 

 zincite in the vicinity of Franklin N.J. where it is mined for zinc. 



Phenacite F»e„Si0 4 



Phenacite is the orthosilicate of beryllium. It occurs in 

 transparent hexagonal crystals, trirhombohedral. which are 

 commonly small, lens-shaped and transparent and white or yel- 

 lowish in color. 



It occurs with microcline, beryl, quartz and topaz and is found 

 in the Urals, in Mexico and at Pike's peak Col. It is sometimes 

 cut for an imitation gem. 



Dioptase H 2 CuSi0 4 



Dioptase is a basic copper orthosilicate occurring in rhombo- 

 hedral crystals and crystalline aggregates of a vitreous luster 

 and emerald-green in color; also massive. 



Wernerite (scapolite) 



Wernerite is an aluminium, sodium and calcium chlorosilicate 

 of variable composition, usually containing some soda. 



The crystals of wernerite are tetragonal, of the general type 

 shown in fig. 219, and are characterized by the low pyramidal 

 termination. They are commonly coarse and thick, often with 

 rounded edges and angles and with a characteristic fibrous 

 appearance on the cleavage surfaces. Wernerite also occurs in 



