APOl'HYLLITK. 



16& 



STILBITE. 



In right rectangular prisms, more or less modified 

 age perfect parallel with M. The prism is usually 

 flattened parallel with the cleavage face, (annex- 

 ed figure,) and terminates in a pyramid ; a : a = 

 119 \ Also in sheath-like aggregations and thin 

 columnar. 



Color white ; sometimes yellow, brown or red. 

 Luster of cleavage face pearly, of other faces vitreous. Sub. 

 transparent to translucent. H = 3*5 — 4. Gr = 2*13 — 2*15. 



Composition: silica 57*6, alumina 16-3, lime 8 9, water 

 16*3. Before the blowpipe fuses with intumescence to a 

 colorless glass. Does not gelatinize except after long boil- 

 ing in nitric acid. 



Dij\ Distinguished from gypsum like heulandite ; and 

 from heulandite by its crystals, which are usually thin, elon- 

 gated rectangular prisms, with pyramidal terminations, often 

 uneven in surface. 



Obs. Occurs mostly in amygdaloid ; also on gneiss and 

 granite. 



It is found sparingly- at the Chester and Charlestown sy- 

 enite quarries, Mass., at Thatchersville and Hadlyme, Ct., 

 at Phillipstown, N. Y., at Bergen Hill, N. J., in trap, in the 

 copper region of Lake Superior, in amygdaloid. In beauti- 

 ful crystallizations at Partridge Island, Nova Scotia. 



The name stilbite is derived from the Greek stilbe, luster 



APOPHYLLITE. 



Dimetric. In right square prisms or octahedrons. Cleav- 

 age parallel with the base highly perfect. Prisms 

 often terminate in a sharp pyramid, (annexed fig- 

 ure,) a : a=104^ 2 and 121 \ Massive and fo- 

 liated. Color white or grayish ; sometimes with 

 a shade of green, yellow, or red. Luster of P 

 pearly : of the other faces vitreous. Transparent 

 to opaque. H = 4*5—5. Gr=2-3— 2*4. 



Composition: silica 51*9, lime 25*2, potash 5*1, water 

 16*0. Exfoliates and ultimately fuses to a white vesicular 

 glass. In nitric acid separates into flakes and becomes 

 somewhat gelatinous and subtransparent. 



What is the crystallization of stilbite 1 What are its general char- 

 acteristics? How is it distinguished ? What is the form and de*Yage 

 of crystals of apophyllite ? What are its other characters ? 



