■58 THE MINERALS OF TASMANIA. 



known to have various types of terminations from a single 

 face (clinadome 5) to as many as six or seven terminal 

 planes. The lode outcrop of the Central Dundas Mine was 

 of considerable height above the natural surface, and 

 through its ferruginous mass large isolated crystals of 

 crocoisite were found. They were often intimately mixed 

 with masses of chalcophanite and manganese oxides. This 

 wonderful find is now practically exhausted, and it would 

 need much exploratory work to attempt to discover another 

 patch. The species has only been reported to occur, and 

 then in extremely limited quantity, at the Colonel North 

 and Silver Queen Mines on the Zeehan Field. At both 

 mines it was obtained as small crystals in gossan. A small 

 quantity is said to have been detected at Broken Hill, 

 New South Wales, and it is known to occur in association 

 with free gold in Western Australia. 



The origin of the chromic acid of the crocoisite has 

 hitherto been somewhat of a mystery, but it may be 

 explained by the presence in the undolomitised websterite, 

 in which the Magnet lode occurs, of numerous irregularly 

 dispersed well-formed crystals of picotite (chrome spinel) 

 of an intense black colour and high lustre, which on decom- 

 position have doubtless afforded the chromic acid essential 

 for the secretion of the chromate. The Magnet silver-lead 

 bearing fissure lode occurs in a dyke of more or less, but 

 generally completely dolomitised websterite rock, which 

 traverses slates of Cambro-Ordovician age. The lode-filling 

 essentially consists of dolomite, siderite, ankerite, and 

 rhodocrosit-e, usually arranged in remarkably regular ver- 

 tical laminations with a central crustification, and in part 

 is not rarely coloured by green chromic acid. The dolo- 

 mitisation of the websterite would appear to have had 

 the eJBfect of decomposing the picotite, as no trace of this 

 mineral is observable where the alteration is well advanced, 

 but the whole is distinctly stained in numerous places 

 throughout the mine a more or less intense green colour 

 by C O.^. The Heazlewood occurrence of crocoisite is like- 

 wise in a lode, occurring intimately associated with green 

 chrome-stained dolomite. The picotite at this locality 

 occurs plentifully distributed in the adjacent serpentine; 

 so much so that it may be collected in considerable quan- 

 tity in the detrital material in the streams. 



At Dundas the metalliferous lodes from which the 

 mineral has been collected in such remarkable profusion 

 and unusual development are closely connected with an 

 intensely groen serpentine rock, in which the chrome-bear- 



