202 THE MINERALS OF TASMANIA. 



north side of the Heazlewood River, than at any other 

 recorded locality. It is found at the Heazlewood in con- 

 nection with the serpentine of the locality, coating the 

 walls of irregular fractures and incrusting the minerals 

 connected with that rock, and always more or less in 

 association with a highly nickeliferous variety of pent- 

 landite. It has been reported to occur in limited quantity 

 at Texas, Pennsylvania, U.S.A.; in Galicia, in Spain; at 

 Unst, Shetland Isles; and a few other localities. 



350. Zeolites. 



These are a well-marked series of crystalline hydrated 

 silicates, all containing aluminium, but in the great 

 majority a proportion of calcium or sodium, or in many 

 cases both, are present. They result from the alteration 

 of felspathoid minerals and felspars. Many are somewhat 

 unstable, and sometimes merge into each other. The 

 hydration may occur as water of crystallisation, but also 

 as hydroxyl belonging to the silicate molecule. They are 

 remarkably plentiful, both as to quantity and species, in 

 basic amygdaloidal rocks, although they are not unknown 

 in mineral veins. The nephelinite of the Shannon Tier 

 produced several fine species, all of an immaculate milk- 

 white. The basaltic rocks of Middlesex, Patersonia, Derby, 

 Bischoff, and elsewhere in the island are replete with more 

 or less fine examples of these model crystallisations. The 

 Mesozoic diabase, M^hich is so pronounced a feature in the 

 geology of the island is not without interest from a zeolitic 

 aspect. The phonolitic complex of Port Cygnet affords a 

 few forms, and the same is the case with respect to the 

 trachydolerite of Table Cape and Circular Head. 



See Analcite, Chabasite, Gmelinite, Hydronephelite, 

 Laumonite, Mesolite, Natrolite, . Phacolite, Phillip- 

 site, SCOLECITE, S'TILBITE, ThOMSONITE. 



351. Zeuxite ( Ferriferous Tourmaline). 



A peculiar variety of tourmaline of a dark-green colour 

 and tufted habit. It is remarkably characteristic of the 

 tin occurrence at Mt. Bischoff, where it is found in vast 

 abundance, often forming rockmasses of considerable size. 

 Its common habit is as short acicular crystals, which are 

 irregularly interlaced together. It is found at the Stan- 

 ley Eiver tinfield in considerable quantity, and it has also 

 occurred at one or two localities at North Heemskirk in 

 connection with the tin lodes there. At the Stanley River 

 it is also found pseudomorphous after orthoclase felspar. 



