ALUMINA. 



347 



This mineral can in general be distinguished from stilbite by the difference in its crystalline 

 form, but especially by the high pearly lustre of the terminal plane. 



Composition. Silica 59.95, alumina 16.87, potash 7.19, water ]5A0{Walmstedt). 



Geological Situation. Similar to that of stilbite, with which it is usually associated. 



Westchester County. This mineral is said to have been found near West-Farms, asso- 

 ciated with stilbite and epidote ; but I have not been so fortunate as to meet with well cha- 

 racterized specimens. I cannot doubt, however, that it will be found in the trap and gneiss 

 ranges in the southern part of the State, as most of the other minerals of this family are already 

 known to occur in them. Small but very brilliant and perfect crystals of the primary form 



(Fig. 334), and of those modified as in Fig. 



Fig. 335, 



Fig. 336. 



335 and 336, occur in cavities in the trap 

 at Bound brook, New-Jersey. They are 

 here introduced for the sake of future com- 

 parison. The same mineral is found at 

 Paterson, New- Jersey. M on a 146° 30'; 

 T on a 148°; P on a 111° 56'; M on / 

 114° 20'. 



In Massachusetts, heulandite has been found at Chester ; and in Connecticut, at Hadlyme. 



EPISTILBITE. 



EpistUbitc. Phillips, Beudant, Shepard, and Dana. — Diplogener, Kuphon-Spath. Mohi. 

 Description. Colour white or yellowish. It occurs regularly crystallized. Sometimes 



Fig. 337. 



Fig. 338. 



M 



M 



also massive. Primary form a right rhombic prism. 

 Fig. 337. M on M' 135° 10'. Often in twin 

 crystals. Cleavage highly perfect parallel with 

 the shorter diagonal of the prism. Fracture in 

 other directions uneven. Fig. 338 is one of the 

 secondary forms. M or M' on t 122° 9'; t on s 

 141° 47'; « on f 109° 46'; i on m 154° 51'. Lus- 

 tre vitreous, except on the faces of cleavage and the 

 corresponding crystalline planes, which are pearly. 

 Transparent to translucent on the edges. Hard- 

 ness from 4.0 to 4.5. Specific gravity from 2.20 to 2.25. Before the blowpipe, it melts, 

 becomes white, intumesces, and forms a blebby enamel ; with soda, it fuses into a transparent 

 glass. It forms a jelly with acids, and the solution is precipitated by oxalate of ammonia. 



Composition. Silica 58.59, alumina 17.52, lime 7.56, soda 1.78, water 14.00 {Rose). 



