112 THE MINERALS OF TASMANIA. 



*' white " iron pyrites. It is practically dimorphous with 

 ordinary pyrite, but is often contaminated with arsenic, 

 which element replaces portion of the sulphur. It crj^stal- 

 lises in the orthorhombic system with the primary form 

 of the right rhombic prism, with numerous modifications. 

 It often occurs in reniform and botryoidal masses, and at 

 times assumes a capillary habit. In colour it varies from 

 a pale bronze-yellow to almost tin-white. It readily 

 decomposes, and is the parent of several sulphates of iron. 

 Alterations to limonite, sphalerite, and other minerals are 

 recorded, and pseudomorphs are common. It occurs after 

 wood at Cox's Bight and elsewhere. The rounded concre- 

 tions of the " orbicular " rock which occurs in the vicinity 

 of the Magnet Mine are at times transmuted to this 

 mineral, while at Beaconsiield Teritar^' fossil -fruits, m3t 

 with in the deep auriferous alluvial, are similarly altered. 

 In the stanniferous drift of Cape Barren Island these 

 fossil-fruits have also been found, and are in many 

 instances altered in the same manner. Marcasite is appar- 

 ently of comparatively recent origin, and is of common 

 occurrence in connection with clay, lignite, and the coal 

 measures. 



It often occurs in the Mersey and Don coal measures ; 

 at Beaconsfield, Scamander River, and many other 

 localities. 



193. Marialite (Hydrous Silicate of Aluminium and 

 Calcium,). 



This is a member of the scapolite fara.ily. Its mode of 

 crystallisation is in the tetragonal system, but it is com- 

 monly in the massive state. 



This mineral was obtained as loosened rounded boulders 

 from a vein in a seam of asbestos occurring in the serpent- 

 ine at Anderson's Cteek, near Beaconsfield. It was mis- 

 taken by the miners for quartz, which it somewhat 

 resembles. It has, however, a slightly greenish tinge, and 

 its hardness is only between 5 and 6. It is soluble with 

 dilTiculty in H CI. 



Microscopical characters confusedly crystalline, with 

 the larger crystal faces obscurely divergent. The crystals 

 often form rosettes. Double refraction higher than quartz. 

 Extinction straight in longitudinal sections. No sensible 

 absorption. 



Scapolite occurs mostly in metamorphosed rocks, ophites, 

 amphibolites, gneiss, and altered gabbro. At Anderson's 

 Creek its occurrence is probably due to vein-forming pro- 



