APOPHYLLITE. 16ft 



STILBITE. 



In right rectangular prisms, more or less modified cleav 

 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 =2-1 3 — 2* 1 5. 



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. 



Dif. 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 Thatch ersville 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 ilspyage 

 of crystals of apophyllite ? What are its other characters'? 



