352 



DESCRIPTIVE MINERALOGT. 



ANALCIME. 



[From the Greek o, privative, and aXxos, strength ; in allusion to its weak electric virtue.] 



Analcime. Hady, Cleaveland, PliiUips, Beudant, Thomson and Shepard. — Hexahedial Zeolite. Jameson. — 



Hexaedrischcr Kuphon-Spath. Mohs. 



Description. Colour white, grey and reddish white. It occurs 

 regularly crystallized ; also in angulo-granular concretions, and mas- 

 sive. Primary form a cube. Fig. 346. Cleavage parallel with the 

 planes of that solid obtained with difficulty. Fracture uneven or con- 

 choidal. Lustre shining, between vitreous and pearly. Ranges from 

 transparent to translucent. Hardness 5.5. Specific gravity from 

 2.27 to 2.53. Before the blowpipe on charcoal, it fuses without in- 

 tumescence into a clear glassy globule ; with borax, it is very difficultly 



soluble. It gelatinizes in muriatic acid. The solution, after the separation of the silica, 



gives an abundant precipitate with ammonia. It becomes feebly electric by friction. 



Analcime is distinguished from leucite, which it resembles, by the difference in crystalline 



form, and by its fusibility ; and from garnet, by its inferior hardness and specific gravity. It 



wants the pearly lustre of stilbite and heulandite. 



Composition. Silica 55.07, alumina 22.22, soda 13.71, water 8.22 {Connel). 



Geological Situation. In New- York and New-Jersey, it occurs in veins in greenstone 

 and gneiss, and is usually associated with other zeolitic minerals. 



localities. 



Fig.347. 



^'s-3<8. Westchester County. Small but very 



perfect trapezoidal crystals of analcime (Fig. 

 347) are found in the gneiss near Yonkers. 

 It is associated with the cuhoide form of cal- 

 careous spar and crystallized iron pyrites. 

 Crystals of the same form also occur in the 

 greenstone at Bergen hill, New-Jersey, 

 Sometimes each angle of the cube is re- 

 placed by three planes, as in Fig. 348, by which twenty-four planes are added to it. When 

 these twenty-four planes are increased to their utmost extent, so that no part of the primary 

 planes is visible, the result is a solid bounded by twenty-four equal and similar trapeziums, 

 called the icositetrahedron. 



