166 ALUMINA. 



Dif. The acute pyramidal terminations of its glass} 

 crystals at once distinguish it from the preceding, as also its 

 cleavage across the prism. 



The name alludes to its exfoliation before the blowpipe. 



Obs. Found in amygdaloidal trap and basalt. 



Occurs in fine crystallizations at Peter's Point and Part- 

 ridge Island, Nova Scotia, and at Bergen Hill, N. J. 



LAUMONITE. 



Monoclinic. In oblique rhombic prisms ; M : M=86 ■ 

 15, P : M=68° 40. Cleavage paraUelto the acute lateral 

 edge ; also massive, with a radiating or divergent structure. 



Color white, passing into yellow or gray. Luster vitre- 

 ous, inclining to pearly on the cleavage face. Transparent 

 to translucent. H=3*5 — 4. Gr=2'3. Becomes opaque 

 on exposure, and readily crumbles. 



Composition: silica 51*1, alumina 21*8, lime 11 9, water 

 15*2. Intumesces and fuses to a white frothy mass. Ge- 

 latinizes with nitric or muriatic acid, but is not affected by 

 sulphuric unless heated. 



Dif. The alteration this species undergoes on exposure 

 to the air, at once distinguishes it. This result may be pr» 

 vented with cabinet specimens, by dipping them into a soli 

 tion of gum arabic. 



Obs, Found in amygdaloid and also in gneiss, porphyrj 

 and clay slate. Peter's Point, Nova Scotia, is a fine locality 

 of this species. Occurs also at Phipsburg, Me. ; Charles 

 town syenite quarries, Mass. ; Bergen Hill, N. J. ; in the 

 amygdaloid of the copper region, Lake Superior. 



Leonhardite resembles laumonite ; it contains silica 55, alumina 24*1* 

 lime 10-5, water and loss 1230. 



^ 



NATROLITE. 



Trimetric. In right rhombic prisms, usually slender and 

 terminated by a short pyramid ; M : M-==91° 10' ; e : 

 e~143 D 14', M:e=116 3 37'. Cleavage perfect 

 parallel with M. Also in globular, stellated, and di- 

 vergent groups, consisting of delicate acicular fibers, 

 the fibers often terminating in acicular prismatic 

 crystals. 



Color white, or inclining to yellow, gray, or redr 



How is apophyilite distinguished? What are the characters of zra- 

 monite ? What takes place when it is exposed to the air ? What ia 

 the crystallization of natrolite ? mention other characters. 



