68 TASMAXIAN MINERALS. 



14 DuFRENiTE {Basic ferric phosphate.) 



Occurs as a thin incrustation of an olive to blackish- 

 green colour on zinc-bearing gangue at the Bell's 

 Reward Mine, Heazlewood. 



15 Emboli'ie {Chlorohromide of silver.) 



In minute but perfectly cubical crystals, which are 

 occasionally octrahedrous. Occurs in a seam of 

 gossan at the Magnet Silver Mine, Magnet. 



16 Felspar {Poly silicates of aluminium potassium, d^c.) 

 The following note on this important group is kindly 



supplied by Mr. W. H. T^yelvetrees, Government 



Geologist : — 



Orthoclase occurs in our granites, syenites, elvans, 

 and quartz porphyries. The most common com^ 

 combinations are (010), (110), (001). Carlsbad 

 twins [twinning plane parallel to the orthopina- 

 coid] (100) are frequently seen. The crystals 

 are generally turbid from decomposition into 

 kaolin, or muscovite. Replacement by pinite 

 chlorite, &c., has occasionally taken place. 

 Porphyritic crystals of an inch or two in length 

 are common in the granite of the East and 

 North-East Coasts. 

 Sanidinc. — This pellucid monoclinic felspar is 

 found in the alkali syenites and elaeolite 

 syenite porphyries of Port Cygnet. It fre- 

 quently shews zonal structure. 

 Plagioclase Felspars, albite, oligoclase, andesine, 

 labradorite, bytownite, anorthite, form a continu- 

 ous series, in which, according to Tschermak, 

 albite and anorthite are opposite extremes. The 

 intermediate felspars have been shewn by 

 Schuster to be isomorphous mixtures of albite 

 and anorthite. 

 Alhite occurs as replacement of the groundmass of 

 porphyroids or keratophyres at Mount Read; in 

 larger crystals in the actinolitised slates in the 

 North Dundas District. Inltergrown with ortho- 

 clase, it forms microperthite ; seen in granite at 

 Anderson's Cteek and in alkali syenite at Port 

 Cygnet. 

 Lahradorite is the felspar of our basalt and dolerite 

 (diabase). Labradorite-bytownite and bytown- 

 ite-anorthite felspars characterise the gabbros at 

 the Heazlewood, Bald Hill, &c. 



