350 On Primary Ores of Iron. 



haps they may augment the quantity : but the trouble fledef- 

 fary to flrip them mud, and ought to., prevent its been ever 

 put in practice. 



III. On Primary Ores of Iron. By Mr. David Mushet, 

 of the Clyde Iron Wbrhs. Communicated by the Author. 



P, 



J II MARY ores of iron are fo named in eontradiflinclion 

 to ores which appear, like iron-ftones, to have been formed bv 

 a lecondary agency. Their varieties are flill more numerous 

 than thofc of iron-ftoncs ; poffefiing various chara&eriftic 

 features, which amply diftinguifh them from each other, 

 either in their inherent properties and effects, or in the man- 

 ner of their foflil difpofition. Some are obedient to the mag- 

 net, others not. This property is by no means dependent 

 upon the quantity of iron exifting in the ore: the ore from 

 the ifland of Elba, fome of which j ields 70 to So per cent, of 

 iron, is (lightly obedient to the magnet: the fine haematites 

 and kidney o£theCumbl rland ore, which yield from 64 to 

 70 per cent, are not, in their native ftate, in the lcait degree 

 magnetic; while many of the Danifh and Norwegian ores, 

 containing from 18 to 30 per cent, are magnetic in a great 

 degree. I have formerly mentioned, that where the magnetic 

 property was inherent, it was more a proof of the exigence of 

 iron, than a criterion whereby to judge of the probable quan- 

 tity of metal in the ore. 



The colours which primary ores of iron exhibit are alfo 

 very various. The beautiful cryitallifcd fractures of the Elba 

 fpecimens, the priftnatic colours they exhibit, the coloured 

 oxydc depoiited in flowers upon their furfacc, and the general 

 appearance which they have of fufion, ftrongly lead to a con- 

 clufion that fire has here been the immediate agent in the 

 production of fuch variegated forms. This conclufion is ftill 

 more forcibly impreffed, after minutely examining and com- 

 paring with them thofe very perfect cryftals which are found 

 5 amongft 



