Mamesian arid Aluminous Rocks, 183 



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in nature than was formerly supposed. Berthier long since gave 

 the name of bauxite to an earthy pisolitic ore which occurs either 

 massive or imbedded in limestones of tertiary age, at Baux, and 

 many other localities in the departments of Gard and Var, and 

 also in Calabria, and the Grecian Archipelago, forming in some 

 places an abundant rock.* This substance is a variable mixture of 

 a hydrate of alumina, apparently approaching diaspore in compo- 

 sition, with hydrous peroxyd of iron, sometimes constituting a 

 workable iron ore, and at other times a veritable ore of alumina. 

 It contains besides small portions of silica, titanic, vanadic, and 

 phosphoric acids, and occasionally encloses grains of corundum. A 

 compact dark red variety gave Deville, alumina b^'Q^ peroxyd of 

 iron 25-3, and water 10*8, besides 3-1 of titanic acid, and 2*8 of 

 silica. In other specimens the proportions of alumina and iron 

 oxyd are nearly equal, or the latter predominates, as in one ex- 

 ample where the proportions were 48'8 of iron oxyd, and 32*2 of 

 alumina ; and another, 60 of iron, and 18 of alumina and titanium. 

 In these analyses the carbonate of lime, generally present, was 

 first removed by a dilute acid ; the prolonged action of stronger, 

 acids completely dissolves the hydrated oxyds. By an intense 

 heat this substance is converted into crystalline corundum, re- 

 sembling emery in its physical character, but the presence of grains 

 of corundum in the hydrated mineral seems to show that the trans- 

 formation may take place at ordinary temperatures. The emery of 

 Greece and Asia Minor, which is associated with variable propor- 

 tions of oxyd of iron, is according to Dr. J. Lawrence Smiths 

 always more or less hydrated. 



The aro-illaceous matter enclosino; some varieties of this bauxite 

 or impure diaspore, is white, without plasticity, and very rich in 

 alumina; one specimen freed from the red ferruginous portions,gave 

 alumina 58-1, silica 21*7, peroxyd of iron 3*0, titanium 3*2, water 

 14-0. This substance approaches in its composition to collyrite, 

 and the dillmite which is the gangue of the diaspore of Schemnitz. 

 These materials however contain from 20 to 40 per cent, of water. 

 Scarbroite, schrotterite, and allophane are similar matters ; the 

 latter, unlike a clay in its structure, appears to have been de- 

 posited from solution. The subsulphate of alumina, known as 

 websterite or aluminite, is often met with in layers and concre- 



* Deville. Ann. de Chime et Physique, (3) Ixi. 309. 



