Lieut-Col. Yorke on Brcmm Iron Ore, 267 



by Kobell was from Oberkirchen in Oldenbourg; it was 

 crystallized, but the crystals were not measurable. This is 

 undoubtedly the same species that 1 have just described. 

 Under the second name is included a substance of the same 

 composition apparently as the first, but from the observations 

 of Rose it seems doubtful whether it has the same crystalline 

 form*. It is under the name of goethite, however, that our 

 mineral of Lostwithiel, &c. appears in Dana's work. I may now 

 remark, that as the composition of this substance is perfectly 

 analogous with that of manganite (MngOg + HO), so are the 

 crystals plesiomorphous; the primary form of manganite being 

 a right rhombic prism of 99° 40', and the ratio of its terminal 

 to its lateral edges is as 25 to 21 (Levy). The secondary 

 planes also, which appear on the figures 1 and 2, are found on 

 the crystals of manganite, as may be seen by examining the 

 figures of that mineral in the works of Phillips and Levy. 



Kobell comes to the conclusion that there are in nature 

 two hydrates of the red oxide of iron, viz. Fcg O3 4-HO, and 

 2 FegOg + 3 HO: the first very rare, the second common. 

 My observations lead me to believe that the first is by no means 

 uncommon in England, as appears by the following examina- 

 tion of brown iron ore from different localities. 



a. Compact brown iron ore accompanied by very minute 

 crystals from the Forest of Dean. Specific gravity obtained 

 from a fragment 4*11. It contained 1 per cent, of silica, and 

 deducting this lost 9*8 per cent, by ignition. 



/3. Fibrous brown iron ore, part of a stalactite, from the 

 same locality as the last; sp. gr. 4*22: loss by ignition 9*41 

 in 100. 



y. Fibrous brown iron ore from Cornwall; sp. gr. 4*19; 

 loss by ignition 1 0*24 in 100. 



These specimens, then, all appear to belong to the same 

 species, FegOg + HO. 



B. 



1 then examined a specimen, also from Cornwall, which was 

 partly compact and breaking into smooth splintery fragments, 

 and partly earthy. The sp. gr. taken on a fragment = S*71j 

 taken from the powdered mineral = 3*98. 8 grs. dissolved in 

 muriatic acid and examined for alumina gave a barely per- 

 ceptible precipitate of that substance ; I could not detect any 

 phosphoric acid, but obtained a trace of a white malleable 

 metal, whose sulphuret was soluble in hydrosulphuret of am- 

 monia, and which appeared to be tin. It lost 14 per cent, by 

 ignition. The following was the result of analysis made on 

 10-99 grs. : — 



* According to Levy the forms are not incompatible. — Vol. iii. p. 161. 



