482 



MINERALOGY 



B.B. Exfoliates and curls, fusing at 2-2.5 to a white enamel. 

 Yields water in the closed tube. Decomposed with HC1 without 

 gelatinization, the solution freed from silica yields a precipitate 

 with ammonia (Al), after filtering, the nitrate yields a white pre- 

 cipitate with ammonia carbonate (Ca). 



General description. Crystals are flattened in habit, parallel 

 to b, and usually joined along the same face in parallel positions 

 forming ridges, the top of the ridge being the base and the sides 

 the two forms s and t, which are vitreous in luster, while the strong 



FIG. 502. Heulandite from the Faroe Islands. 



pearly luster on b is very characteristic. The face b is often con- 

 cave, while s and t are convex and striated parallel to their inter- 

 section with b. Sometimes it occurs in globular shapes or granular. 



Chemically the calcium in part may be replaced by sodium, po- 

 tassium, barium, or strontium, when it approaches brewsterite, 

 another very closely related zeolite. 



Heulandite is a very common mineral in the trap of Bergen Hill, 

 and in the quarries at Paterson, New Jersey. Red specimens are 

 found in Nova Scotia ; Fassathal, in the Tyrol. It also occurs in 

 Iceland and the Faroe Islands. 



HARMOTOME 



Harmotome. H 2 (K 2 . Ba)Al 2 (Si0 3 ) 5 . 5 H 2 O; Monoclinic; Type, 

 Digonal Equatorial ; a : b : c = .7032 : 1 : 1.2310 ; p = 55 10' 

 = 001,100; 100,110 = 29 59';' 001 A 101 = 35 42'; 001*011 = 

 45 18'; Common forms, c (001), b(010), a (100), m(110); 



