108 XBW YORK STATE MUSEUM 



It occurs in orthorhombic crystals of prismatic habit which 

 are often twinned, producing crosslike forms (pi. 33 x ). The 

 luster is resinous to vitreous and the color varies from a black- 

 ish brown to dark brown or gray. 



Staurolite is usually found in metamorphic rocks such as 

 gneiss, mica schist and argillaceous schists as a result of regional 

 metamorphism and is frequently associated with garnet, silli- 

 manite, cyanite and tourmalin. It occurs throughout the mica 

 schists of New England, in Xorth Carolina and Georgia. A few 

 occurrences are noted in the mica schists of New York as the 

 result of contact metamorphism, as at Peekskill, Westchester co. 1 



Hydrous silicates 

 The species here included contain water of crystallization, as 

 is the case with the zeolites, or yield, on ignition, water which is 

 present as a base; in the latter category belong the micas and 

 talc. In a third type of silicates referred to this division the 

 relation of the water contained to the general composition is 

 still in doubt. 



Zeolite division 



Apophyllite H T KCa 4 (Si0 3 ) 8 ^H 2 



Apophyllite is a hydrous potassium and calcium silicate. 

 It occurs in tetragonal crystals, mostly of square cross sec- 

 tion, sometimes flattened in the direction of the ver- 

 tical axis into plates; and in rectangular forms, some- 

 what isometric in aspect but striated on the prismatic 

 faces and giving pearly reflections from the basal 

 plane (pi. 33 2 ); it is often found with steep pyramidal 

 terminations (fig. 232). It is also found occasionally 

 in lamellar masses. The luster is vitreous except on 

 the basal pinacoid which face has a pearly luster with 

 internal opalescence often likened to the eye of a 

 fish; it is colorless, white, pink or greenish. 



r lg. £itti 



Apophymte Apophyllite occurs as a secondary mineral in basalt 

 and other volcanic rocks associated with the zeolites, datolite. 

 prehnite, and calcite; also in cavities in granite aud gneiss. 

 Xova Scotia, the Lake Superior copper region and Bergen Hill 

 X. J. afford many ^rood specimens. 



1 Williams. G. H. Contact metamorphism near Peekskill N. Y. Am. 

 jour, scl 1888. 36:254. 



