BY W. F. PETTERD, CM.Z.S. 75 



■unlikely that clear pellucid material may be found if a 

 lookout is kept for such. Occurs at the Oonah Mine, Zee- 

 han, with pyrites and stannite ; it is always more or less 

 associat-ed with quartz. The other known occurrences of 

 this mineral are purely of a minor character, and do not 

 call for any special remarks. 



131. Galen I TE (Sulphide of Lead). 



This mineral — the most abundant ore of lead — is widely 

 distributed over the northern and western portions of the 

 island, occurring in all its many variations of structure, 

 from the steel-grained to the coarse cubical ore, often 

 exhibiting extreme variation in this respect in the same 

 district, or even in the same mine. In geological occur- 

 rence it also varies to a greater extent than almost any 

 other mineral. Here it is common to the tin-bearing 

 granites of Ben Lomond ; to the fossiliferous Silurian 

 slates and sandstones of the Zeehan field ; as well as occur- 

 ring in the dolomitised rocks of the Heazlewood and Mag- 

 net ; and is even found to a limited extent in the aurifer- 

 ous quartz reefs of the Mathinna, Lefroy, and other dis- 

 tricts. From nearly all localities the lead sulphide, as 

 occurring in this State, is characterised by the unusually 

 high assay returns of silver that it yields. As is usually 

 the case in lead-producing countries, the common ore of 

 lead is the sulphide. It crystallises in the cubic system, 

 but the occurrence of crystals in this island is quite 

 exceptional. It admits of remarkably perfect cleavage, 

 readily breaking into cubes. 



Among the minerals bearing paragenetic relationship 

 occurring here are ferrous-carbonate, blende, and pyrites. 

 Except in rare instances, what are known as the " sparry " 

 accompaniments of the Old World lead-mining localities, 

 such as fluorite and calcite, are usually absent. Galena 

 readily suffers decomposition or alteration near the 

 exposed surface, due to the action of oxygen and car- 

 bonic acid, owing to which anglesite, cerussite, and other 

 secondary lead salts are produced by chemical reactions. 

 In rare instances the gradual change from the crystalline 

 sulphide into lead-carbonate and sulphate-carbonate, or, 

 when antimony is present, into bindheimite, is readily 

 detected, the Comet Mine at Dundas affording excellent 

 illustrations of the latter alteration, where the graduation 

 can be distinctly traced. At times, when such an altera- 

 tion does take place, a nucleus of unaltered galena may be 

 found, which is perfectly surrounded by either one or other 



