478 MINERALOGY 



axes are at 60, with 232 as the composition face, are also 

 common. 



In rock sections staurolite is pale yellow to reddish brown, usually 

 in crystalline outline, containing numerous inclusions, often of 

 carbonaceous matter, at times symmetrically arranged. Relief 

 is high, interference colors gray to yellow of the first order. The 

 interference figure is in the basal section. The optic axes lie with- 

 out the field of view. 



It is a product of contact metamorphism, occurring in argilla- 

 ceous shales and schists, associated with eyanite, sillimanite, and 

 garnets. 



Beautiful specimens occur at Pizzo Formo, near St. Gothard, 

 Switzerland, where it is found in a paragonite schist associated with 

 eyanite, often in parallel growths. 



At Windham, Maine, crystals nearly two inches in length are 

 embedded in a mica slate associated with eyanite and small garnets. 

 It occurs also at Franconia, New Hampshire ; at Sheffield, Massa- 

 chusetts, at many points in Connecticut, Virginia, North Carolina, 

 and Georgia. In Lincoln and Fannin counties, Georgia, many sim- 

 ple and twinned crystals lie loose in the soil or in the decomposed 

 schist. It is not easily altered by weathering, but at times forms 

 muscovite, or a steatite-like substance mixed with quartz. 



The synthesis of staurolite, like many other contact and pneu- 

 matolytic minerals, has not as yet been accomplished with cer- 

 tainty. 



ZEOLITES 



The zeolites are a group of hydrated silicates of aluminium with 

 either calcium and the alkalies, or both. Calcium may be replaced 

 by barium or strontium, but there is little or no magnesium. In 

 their occurrence, they are not found as primary minerals, but the'y 

 are all secondary products derived by the hydration of such primary 

 minerals as the feldspars, nepheline, or leucite. They may be 

 found in the mass of the rock containing the minerals of which 

 they are hydration products, or they may be found filling the pores, 

 cracks, and other cavities in which they have been precipitated or 

 crystallized from solution. 



They are common minerals associated with such rocks as dia- 

 base, diorite, syenites, and those containing leucite, nepheline, or 

 sodalite. They are also less commonly found connected with the 

 metamorphosed, or even the semimetamorphosed, sedimentary 



