Lieut.-Col. Yorke on Brown Iron Ore. 265 



When I made the experiments I had not seen the second 

 edition of Dana's Mineralogy*, or the analyses of Kobell 

 quoted therein, or I should probably have saved myself the 

 labour. Although my results accord with those of Kobell, 

 yet as it does not appear that any distinctly crystallized spe- 

 cimen has been analysed, and as the most interesting problem 

 in mineralogy is the connection between crystalline form and 

 composition, it may not be deemed superfluous if I submit 

 my results to the Chemical Society. 



A. Crj/stallized Brown Iron Ore. 



The specimen was obtained from Restoomel mine near 

 Lostwithiel. The specific gravity of the mineral, taken on a 

 crystal weighing 2*504 grs., I found to be 4«'37; when taken 

 from the powdered mineral, in the manner described by G. 

 Rose, it came out 4*22 to 4'24. 



I annex figures of the forms of two crystals, and the mea- 

 surements I have observed on them, together with those of 

 similar angles obtained by Phillips and Levy. Levy makes 

 the primary form a right rhombic prism of 95°* 14, the ratio of 

 whose terminal edges is to that of the lateral edges as 10 to 

 9t ; and I have followed this author in the choice of the planes 

 assumed as primary. 



Fig. 1. agrees perfectly with the view that the primary form 

 is a right rhombic prism ; but with the crystal fig. 2. I met 

 with a difficulty, inasmuch as I obtained as the inclination of 

 g, on a plane apparently corresponding to h^ fig. 1, the angles 

 1 J5°40', and with ^ on the other side 114° nearly. I believe 

 this is owing to there being in reality two very narrow planes, 

 i i'i as I have represented them In fig. 2, meeting at a very 

 obtuse angle, and to my catching the reflexion from one plane 

 only. Could it be from a cause of this kind that G. Rose 

 has referred this substance to his fifth system of crystalliza- 

 tion? J I hope an experienced crystallographer may be in- 

 duced to examine this crystal. 



Composition. — Some preliminary experiments satisfied me 

 that the substance consisted of red oxide of iron, oxide of 

 manganese and water, with small but variable quantities of 

 silica. I could not detect any phosphoric acid or alumina. 



* A System of Mineralogy, by James Dana, 2nd edit., New York and 

 London. 1844. 



f Description d'une Collection de Mineraux formte par M. H. Heuiand, 

 par A. Levy. Londres, 1837. vol. iii. p. 155. 



J Eleviens de Crystallographies par G. Rose, traduit par V. Regnault, 

 p. 261 (18). 



'H'^^mi 



