HIS 



NEW YORK STATE MUSEUM 



It occurs iii orthorhombic crystals of prismatic habit which 

 are often twinned, producing crosslike forms (pi. 33J. 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- 

 nianite, cyanite and tourmalin. It occurs throughout the mica 

 schists of Way England, in North Carolina and Georgia. A few 

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

 result of contact rnetaniQirphism, as at l'eekskill, Westchester co. 1 



Hydrous silicates 



The species here included contain water of crystallization, as 



is i lie 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 (SiO :! ) s 4IIL0 

 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 1 , pink or greenish. 



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 and gneiss. 

 Nova Scotia, the Lake Superior copper region and Bergen Hill 

 X. .1. afford many good specimens. 



1 Williams, (j. ii. Contact nietainorphism near Peekskill N. Y. 

 jour. sci. 1SSS. ;;<!: 254. 



Am. 



