the minerals of new south wales. 193 



Epsomite. 



Chem. Conip. : Hydrated magnesium sulphate. Occurs as an 

 efflorescence in the caves of the Hawksbury sandstone ; usually 

 masses of fibrous crystals are met with sometimes five or six inches 

 in length, of a beautiful white silky lustre. The crystals are 

 usually curved towards the free end ; also in radiate groups of 

 small crystals. Very fine specimens have been obtained from 

 Dabee, Wallerawang, and Mudgee, the Great Western mines, Icely, 

 and Barragorang. 



Magnesite. 



Chem. Comp. : Magnesium carbonate. Crystallizes in the 

 hexagonal system, usually as rhombohedra ; but no well-developed 

 crystals have yet come under my notice. It is most commonly found 

 massive, or in concretions, having a mammillated or botryoidal 

 form. H. = 4 to 5. Sp. gr. = 2-94. 



It is found in New England in various places, and upon the 

 Diamond Fields at Bingera, and near Mudgee ; when impure it is 

 of a gray or gray-brown colour, but when pure it is of a dazzling 

 white ; compact, tough, and breaks with a flat conchoidal fracture. 

 It adheres to the tongue, and has a very cold feel like porcelain. 



It effervesces with hydrochloric acid, but with difficulty. 



At the diamond diggings at Two-mile Flat, near Mudgee, pure 

 white magnesite was observed to form by the spontaneous decom- 

 position of the heaps of refuse from the miners' shafts ; pebbles 

 were quickly cemented together by it. 



The late Dr. Thomson of the Sydney University found that the 

 magnesite thus formed, and incrusting rubbish heaps, timber, old 

 tools, etc., had the following composition : — 



Magnesia ... ... ... ... 46-99 



Carbonic acid ... ... ... ... 49*78 



Water 4-08 



100-85 



Sp. gr. = 2-94. 



This magnesite sometimes contained calcite. It was also observed 

 under the same circumstances on Cunningham's Diggings on the 

 east side of Cudgegong Creek, and there with a peculiar vermicular 

 or worm-like form. 



Another locality is the Lachlan Biver. 



Sulphate of Alumina. 



Chem. comp. : Hydrated aluminium sulphate. Commonly called 

 u alum," from its astringent taste, but potassium is absent from the 

 mineral. 



