170 THE MINERALS OF TASMANIA. 



OjJtical Propertie^j in Thin Section. 



Colour — Pale-rose to brownish-rose. 



Pleocliroism — Absent. 



Birefringenee^ — Strong, giving 2nd to 3rd order 

 colours, in section not exceeding 0'03 mm. in 

 thickness. 



Extinction of Fibres — Straight. 



Optical Character (measured with respect to the 

 elongation of the fibres) — Positive. 



Structure — Fibres and tufts, sometimes curved, radi- 

 ally disposed about nuclei of chromite. The 

 radiating aggregates are wrapped round with a 

 mosaic of small scales and fibres. 



" Note. — Optical properties require further investigar 

 tion. Only one thin section available for examination." 



309. Steargillite (Hydrous Basic Silicate of Alu- 



7ninium). 



An unsatisfactory clay-like mineral that is apparently 

 allied to t'he above occurs in the vicinity of Derby. It is 

 a pale-yellow, almost white, substance, with a strongly con- 

 choidal fracture, and slightly opalescent, smooth surface. 



310 Steatite (Hyclrated Silicate of Magnesium). 



This is more generally known as soapstone. It is the 

 massive variety of talc, with a characteristic soft unctuous 

 feel, and is so soft that it yields to the nail. It is first 

 in the scale of hardness. It is a very abundant substance, 

 and is useful for m.any minor industrial purposes. 



It is abundant in connection with serpentine, Asbestos 

 Mountain ; also known to occur at the following, among 

 other places: — Mt. Bischoff ; Heazlewood ; Mt. Claude; 

 and near Beaconsfield. 



311. Stephanite (Sidyhide of Silver and Antimony). 



This well-marked species is orthorhombic in crystallisa 

 tion, occurring either as short prisms or as tabular crys- 

 tals, which ara often niackled, but is commonly massive 

 or in clus4]ers. It is soft and sectile. Known also as 

 brittle silver ore. It is black and dull in appearance, with 

 a black streak. It is found in thin irregular patche^^^ 

 implanted on a siliceous gangue, often in company with 

 ^' fire blende," at the Long Tunnel Mine, Castray River ; 

 it has also occurred at the Owen Meredith Mine implanted 



