112 MINERALS AND GEOLOGY 



68. Datolite : White or pale-green. Clinorhombic in crystalliza- 

 tion, but occurring chiefly in botryoidal masses of fibrous structure. 

 H = 5.0 5.5 ; sp. gr. 2.95 3.0. BB tinges the flame pale-green, 

 and melts with great bubbling. In the bulk-tube yields about 5 per 

 cent, water. Gelatinizes in hydrochloric acid. Average composition : 

 silica 38, boracic acid 21.5, lime 35.5, water 5.0. Of doubtful 

 presence in Central Canada, but bel red to occur sparingly in some 

 of the trap rocks of Lake Superior. Abundant on the south shore 

 of the lake, and present also on Isle Royale. 



69. Laumontite : White, greyish, pale-red, &c. Clinorhombic but 

 mostly in fibrous groups. H = 3.5 4.0, but often less from 

 incipient decomposition of the mineral; sp. gr. 2.2 2.35. BB, 

 exfoliates, and melts to a white enamel. Gives off" a large amount 

 of water in the bulb-tube. Gelatinizes in hydrochloric acid. Aver- 

 age composition : silica 52, alumina 21, lime 12, soda 4.5, water 

 15. Occurs in the amygdaloidal traps of Lake Superior, but 

 mostly in a weathered condition. 



70. Thomsonite : White, red, &c. Rhombic, but most common- 

 ly found in indistinct acicular crystals and fibrous groups. H 5.0 

 5.0; sp. gr. 2.3 2.4. BB, intumesces, and melts into a blebby 

 glass. Gives off water in the bulb-tube. Gelatinizes in hydrochloric 

 acid. Average composition : silica 38, alumina 30, lime 1 3, soda 

 4.5, water 13.5. Of somewhat doubtful occurrence, but some of 

 the zeolites from the amygdaloidal traps of Lake Superior belong 

 apparently to this species. They are mostly in a weathered and 

 semi-decomposed condition. 



71. Heulandite. 72. Stilbite. 73. Chabazite. These minerals 

 are essentially hydrous silicates of alumina and lime. They are said 

 to occur in some of our trappean rocks, but nowhere in distinct or 

 well-characterized examples. 



SUB-GROUP B : ALKALINE ZEOLITES. 



Natrolite : White, yellowish, &c. Rhombic in crystallization, 

 but occurring most commonly in radiating fibrous groups. H = 5.0 

 5.5 ; sp. gr. 2.15 2.35. BB, tinges the flame strongly yellow, 

 and melts very easily without intumescence. In the bulb-tube, yields 

 a large amount of water. Gelatinizes in acids. Average composi- 

 tion : silica 47.5, alumina 27, soda 12, water 9.5. Occurs, but 

 mostly in a weathered condition and in part altered into carbonate of 



