BY W. F. PETTERD, C.M.Z.S. 139 



252. Pleonaste (Aluminate of Magnesium and Iron). 



Also known as black spinel and as ceylonit-e. It is 

 intensely black, opaque, and has a high polish with a 

 strong conchoidal fracture. It is one of the minerals 

 termed " black-jack " by the north-eastern tin miners. 

 It is extremely abundant in the alluvial tin-drift, usually 

 occurring as waterworn lumps of small size, and but rarely 

 showing any indication of crystal outline. It is commonly 

 associated with zircon, sapphire, and quartz. 



It is plentiful at Weldborough, Moorina, Branxholm, 

 Mt. Cameron, Hampshire, in small pieces at the Blythe 

 River, and in small quantity at the Denison goldfield. 

 The red and other coloured spinels are not known to occur 

 in this island. 



253. Plinthite (Hydrous Silicate of Aluminium). 



An amorphous clay-like substance of a brown colour, 

 with conchoidal fracture, but of doubtful homogeneity, 

 being in all probability but an indurated mixture. It 

 occurs near Falmouth. 



254. Plumbogummite (Hydrated Phosphate of Lead and 



Aluminium ) . 



Occurs in stalactitic and irregular globular and botry- 

 oidal forms of a pale-brown colour, with a resinous lustre. 

 It was found attached to partially decomposed gakna at 

 the British-Zeehan Silver-lead Mine. 



255. PoLYSPHOERiTE (Hydrated Phosphate of Lead and 



Calcium). 



This mineral occurred as minute rounded pellets, which 

 had an internal radiated structure. Colour brown, with 

 a somewhat greasy appearance. It was found intimately 

 associated with bunches of pyromorphite and cerussite at 

 the Sylvester Silver Mine, Zeehan (A. J. Taylor). 



256. PoRCELLANiTE (SiHcate of Aluminium). 



This is a milk-white, compact, and smooth porcelain- 

 like substance, with a glimmering conchoidal fracture. 

 It is not strictly a mineral species, but is apparently an 

 indurated clay. It occurs sporadically in the vicinity of 

 Mt. Lyell. 



