164 ALUMINA. 



in amygdaloid, and some of them occasionally in granite or 

 gneiss. The first four, heulandite, laumonite, apophyllite, 

 stilbite, have a strong pearly cleavage, and do not occur in 

 fine fibrous crystallizations ; when columnar, the structure is 

 thin lamellar. Excepting laumonite, these species dissolve 

 in the strong acids, but do not gelatinize. The species 

 natrolite, scolecite, stellite, and thomsonite, are often fibrous, 

 and the crystallizations generally slender. The remaining 

 species, harmotome, analcime, sodalite, hauyne, lapis lazuli, 

 and chabazite, occur in short or stout glassy crystals, and are 

 seldom fibrous. To the second division above given might 

 be added the species dysclasite and pectolite, described under 

 Lime. They have a more pearly or silky luster than 

 natrolite. 



HEULANDITE. 



Monoclinic. In right rhomboidal prisms and their modi 

 fications. P on M or T=90 . M : T=129° 40'. 

 Cleavage highly perfect, parallel to P. Luster of 

 cleavage face pearly, of other faces vitreous. Color 

 white ; sometimes reddish, gray, brown. Transpa. 

 rent to subtranslucent. Folia brittle. H=3'5 — 4. 

 Gr=2-2. 



Composition : silica 59*3, alumina 16*8. lime 9*2, 

 water 14*7. Intumesces and fuses, and becomes phospho- 

 rescent. Dissolves in acid without gelatizing. 



Dif. Distinguished from gypsum by its hardness and the 

 action of acids and the blowpipe ; from apophyllite and stil- 

 bite by its crystals. 



Obs. Found in amygdaloid ; occasionally in gneiss, and 

 in some metalliferous veins. 



Occurs at Bergen Hill, N. J., in trap ; at Hadiyme, Ut., 

 and Chester, Massachusetts, on gneiss ; near Baltimore, on 

 a syenitic schist ; at Peter's Point and Cape Blomidon 

 Nova Scotia, in trap. 



The species was named by Brooke in honor of Mr. Heu- 

 land, of London. Lincolnite is here included. 



Brewsterite. Crystals right rhomboidal prisms, with a perfect 

 pearly cleavage like heulandite ; but M : T=93° 40'. H=4| — 5 

 Gr=2"l — 25. From Argyleshire and the Giant's Causeway. 



What is the appearance and structure of heulandite 1 How is 

 distinguished from gypsum ? how from apophyllite and stilbite 1 



