FENNER, THE WATCHUNG BASALT 167 



In a hand specimen, there is an association of analcite and natrolite in 

 -what appears to be a reversal of the usual conditions, that is, analcite 

 crusts appear to rest upon natrolite. It is found, however, on close 

 examination, that the analcite crystals are porous and drusy, while the 

 natrolite is fresh, and the crystals show characteristic pyramidal termina- 

 tions. They grow up among and probably through the analcite. The 

 specimen is a good example of the deceptive appearance which replace- 

 ment relations often assume. 



The observations of Brogger^** upon analcite found as a mineral of late 

 development in the Norwegian syenite-pegmatite veins are of interest. 

 He finds that analcite is the oldest and most widespread of all the zeolites 

 found in open vugs and continues his description as follows : 



As Lemberg has ascertained, analcite is formed very easily at the expense 

 of various soda-rich silicates at somewhat high temperature. Friedel and 

 Sarasin" obtained beautiful crystals of analcite by heating the ingredients of 

 albite with water up to 400° ; A. de Schulten" obtained, by 18 hours' heating 

 of a solution of soda silicate or of soda in closed tubes of an aluminous glass 

 at 180°-190°, analcite crystals up to 0.1 mm. in size, also^* by heating (during 

 17 hours up to 180° ) soda silicate and soda aluminate in the proportions cor- 

 responding to the composition of analcite in lime-water in closed copper tubes. 

 We recall further that among the soda-rich zeolites of Plombieres observed by 

 Daubrge (where the thermal waters, which have here deposited zeolites in 

 recent times, show only about 70°), analcite was not found, so we may almost 

 venture to estimate the temperature at which the abundant deposition of 

 analcite in our veins ensued at more than 70°, perhaps at about 200°. 



The high temperature which Brogger assumes for analcite deposition 

 hardly appears justified for the Watchung rocks, but a considerable de- 

 gree of superheating may well have existed. 



Chaiazite, Heulandite and Stilhite 



Chabazite, heulandite and stilbite are so frequently associated, both in 

 hand specimens and in the slides, that they may very well be considered 

 together. In the larger specimens, they are among the most abundant 

 minerals and frequently form showy groups. The chabazite crystals are 

 usually of a light salmon or salmon-pink color, and in general show only 

 rhombohedral faces (or pseudorhombohedral, if this view be taken). 

 Heulandite sometimes exhibits pink tints but more frequently is almost 

 colorless. Single crystals occur, but grouped forms with curved faces, 



w Zeitschr. fxir Kryst. und Min., vol. 16, p. 169, 1890. 

 " Compt. rend., vol. 97. p. 290, 1883. 

 " Bull, de la soc. min. de France, vol. 3, p. 150, 1880. 

 "/bid., vol. 5, p. 7, 1882. 



