70 TASMANIAN MINERALS. 



structure poicilitic, enclosing apatite, fluoi;. iron 

 oxide, &c., and pierced with quartz grains; often 

 suiTounds felspar plates. Professor Rosenbusch, in a 

 letter under date January 12, 1899. mentions this 

 mineral as " a peculiar weakly bi-refringent mono- 

 clinic amphibole, bluish-green in colour; a grey- 

 green h brownish-green, C bluish-gi^een to blue, 2 E 

 (the apparent optical axial angle) small, optical 

 character -f and with strong dispersion of the axes. 

 It recalls strongly the blue-green amphiboles of the 

 crystalline schists in the Scora Vale, in the centre 

 and north of Norway, and elsewhere." 

 The series of phonolitic rocks of Port Cygnet afford one 

 and perhaps two species of soda amphibole, but their 

 specific identification i"; attended with coiasider- 

 able difficulty. Many of the rocks referred to have 

 beem microscopically examined by Professor Posen- 

 busch, and that well-known authority, in a com- 

 munication to Mr. W. H. Twelvetrees. refers to one 

 of the hornblendes as being barkevekitic. This is the 

 prevailing form' which is seen in rock sections from 

 the locality indicated. It is myrtle green in colour 

 by transmitted light, and in the absorption t) > C > a. 

 in this respect appertaining more to kataforit^. but 

 differing in the pleochroism. In the fractures and 

 joints of the elaeolite syenite from the same place a 

 black amphibole is occasionally developed, having 

 much the general appearance of arfvedsonite. It is 

 usually plentiful, occurring as long narrow thin 

 laths and aggregates, sometimes reaching a trifle over 

 2 inches in length; they do not shew terminations, 

 but have an irregular brittle structure. Fragments 

 examined under the microscope shew the substance to 

 be green by transmitted light. It is apparent that 

 the soda hornblendes ait Port Cygnet differ in some 

 degree from those recorded from similar rocks in 

 better known localities, and that they require further 

 investigation before they can be satisfactorily deter- 

 mined. 



21 HiSTT^ixiTE fSnIpJiidr of hixinjifh (tnd aniiinony.) 



This mineral occurs massive at several of the North- 

 East Dundas mines, where it is classed under the 

 common designation of '' Fahl ore," a term applied 

 to several very diglfcinct minerals with the general 

 physical characters of tetrahedrite. 



