82 THE MINERALS OF TASMANIA. 



variety essonite — with actinolite and molybdenite as acces- 

 sory minerals. 



See also Almandite, Aplome, Grossularite, John- 



STONOTITE, MeLANITE. 



133. Genthite (Hydrated Silicate of Nickel and Mag- 



nesium), 



A few small specimens of this nickel gymnite, showing 

 the characteristic apple-green colouration, have been 

 obtained from the workings of the Heazlewood Silver-lead 

 mines. They occurred as a thin incrustation on the dolo- 

 mite veinstone of the lodes. It has also been found 

 sparingly on the pentlandite which occurs in the vicinity 

 of Mt. Agnew. 



134. Gibbsite ( Alumifiium Hydrate). 



This is found as a white incrusting mineral, with an 

 obscure fibrous structure. It also occurs in small coral- 

 loidal aggregations, mamillary patches and prisms, 

 implanted on limonits and manganese minerals, at the 

 Central Dundas, West Comet, and other mines at Dundas. 

 Plentiful as an incrustation, accompanied by native copper 

 and earthy matter, at the Rio Tinto Mine, Savage River. 

 At this locality it varies in colour from clear pellucid to a 

 pale-green, and (more rarely) to golden-yellow with a 

 bronze lustre. It forms a thin seam on the wall of a cop- 

 per lode at the Burnie Copper Mine, Blythe River. This 

 mineral is also known under the name of hydrargillite. 



135. Gilbertite (Altered Potash Mica). 



A common result of the altferation of muscovite is the 

 formation of gilbertite ; this is especially noticeable in the 

 stanniferous granites and porphyries. It might correctly 

 be termed a hydrated muscovite, and thus comes near the 

 substance which has been named margarodite. It varies in 

 colour from yellow to a pale-greenish, and has a glim- 

 mering lustre. At the Shepherd and Murphy Mine, Bell 

 Mount, it often contains embedded crystals of cassiterite 

 and, at times, wolframite. It abounds at most of the tin 

 mines in t'he Ben Lomond and Blue Tier districts 



136. Glauber Salt fSidphate of Sodium). 



Occurs on the floor and walls of caves and shelving 

 saliferous rocks as an efflorescent coating, and is commonly 



