416 RECORDS OF THR AUSTRALIAN MUSEUM. 



ZEOLITES. 



Wherever we find decomposed felspathic rocks we may look for 

 zeolites in their amygdaloidal cavities. Generally several zeolitic 

 species occur together, sometimes forming intergrowths, and, as 

 in crystalline habit, qualitative and even quantitative composition 

 certain zeolites have a strong family resemblance it is not always 

 easy to discriminate between them. In this paper I have confined 

 myself to describing those of whose identity tliere is no reasonable 

 doubt. 



CHABAZITE. 



Ben Lomond, New South Wales. 

 (Plate Ixxix., figs. 1, 2). 



The basalt of Ben Lomond is much decomposed and so full of 

 cavities that in hand specimens it sometimes presents the vesicular 

 appearance of pumice. The smaller cavities are often completely 

 filled with an incoherent, yellowish-green substance which has a 

 clayey odour when wetted ; the powder has not been analysed 

 but is probably bole or some equally indefinite mineral of the 

 kaolin group. Larger cavities are filled with zeolites sometimes 

 beautifully crystallised ; chabazite predominates and is accom- 

 panied by analcite and delicate acicular crystals which are mainly 

 mesolite but may possibly be natrolite in some cases. Yellowish 

 calcite in scalenohedra or in spherical aggregates accompanies the 

 zeolites. The specimens in the Museum collection were obtained 

 by purchase from Mr. D. A. Porter who has also supplied us with 

 particulars of the occurrence.® The specimens were obtained from 

 excavations and cuttings on the Northern Railway line, the finest 

 being found in the " Big Cutting " situated about a mile in a 

 northerly direction from Ben Lomond railway station. 



The chabazite is sometimes crystallised in simple rhombohedra 

 much striated parallel to the edges rjr and rjr" or forms unequal 

 interpenetrating twins with the vertical axis as axis of twinning, 

 but it usually presents the characteristic form of phacolite with 

 the forms r (lOllj, s (0221) and e (0112) twinned on the same 

 law. The crystals, which attain a diameter of 3 cm., are but 

 little inferior to the well-known phacolite of Richmond, Victoria ; 

 they are less regularly developed however, and are strongly 

 striated parallel with the intersections rje. A common feature 

 is a crateriform depression at the apex shown in plan in PI. Ixxix., 

 fig. 2. In such crystals each individual of the twin really consists 

 of three portions in parallel position. 



9 Porter— Journ. Roy. Soc. N.S. "Wales, xxii., 1888, p. 87. 



