167 



Regis. Not seldom plates of ilmenite are seen to be arranged in parallel 

 rows intersecting each other at angles of 60. The theoretical composition 

 of ilmenite is represented by the formula FeTi0 3 , but chemical analyses 

 usually show a certain amount of Fe.,0 3 and it is probable that a perfect 

 series exists between Fe 2 3 and Fe Ti0 3 . Ilmenite and hematite are 

 not attracted by the magnet. The common alteration product of ilmenite is 

 a whitish or yellowish substance which was first described by GUMBEL (1) and 

 named leucoxene. It may be opaque or semi-transparent. In the latter case 

 it shows strong refraction and double refraction. The true character of this 

 alteration product was determined by CATHREIN. (2) He analysed the 

 leucoxene of a rock from the Alpbachthal and found that it possessed the 

 chemical composition of sphene (CaO Si0 2 TiOo). As typical sphene possesses 

 well marked optical characters it seems desirable to retain the term leucoxene 

 for the ill-defined alteration product. The alteration of ilmenite sometimes 

 commences at the margin and proceeds inwards until all trace of the original 

 mineral has disappeared ; at other times it proceeds along two sets of parallel 

 planes which appear to intersect each other at angles of 60" and 120" ; thus 

 etching out as it were a structure that would otherwise escape notice. NEEF (3) 

 found, on treating a certain section of diabase with hot hydrochloric acid 

 that the opaque iron ore was partially destroyed, a fine net-work, due to two 

 parallel series of lamella) iiitergrown so that the angles between them 

 corresponded to the angles of the fundamental rhombohedron remained 

 behind. KUCH (4 > obtained precisely similar results in the case of a similar 

 rock from West Africa. Now, as magnetite is much more readily dissolved 

 than ilmenite, this seems to imply that in these cases the original substance 

 was an intergrowth of these two minerals ; at any rate it proves that 

 the opaque iron oxide was not homogeneous. 



Saussure described under the name of sagenite certain curious reticulated 

 aggregates of rutile (TiO ) in which the angles of the meshes are 60 and 120; 

 and CATHREIN infers the existence of such aggregates in the ilmenite which 

 furnished the leucoxene that he analysed. It is an interesting fact that the 

 reticulated structure so frequently developed in the opaque iron oxides of the 

 dolerites (diabases), as for example in certain portions of the Whin Sill, 

 should so closely resemble in character the sagenite-aggregates of Saussure. 

 The occurrence of rutile in sagenite-form in hematite has been described by 

 GYLLIXG. (S) 



When the opaque iron oxides occur in the form of grains and irregular 

 ragged aggregates it is in many cases impossible to determine whether they 

 should be referred to magnetite or ilmenite. The presence of leucoxeue as 

 an alteration product is not decisive, as this may arise from the decomposition 

 of a titaniferous magnetite. The author found that the iron ores of the 



(1) Die palaolitldschen Eruptivgesteine des Fichtelgebirges. Miinchen, 1874, p. 22. 



(2) Uber Titaneisen, Leukoxen uiid Titauomorphir. Z.K., 1882, VI., p. 244. 



(3) Z.D.G.G. Vol. XXXIV., p. 470. 



(4) T.M.M. Neue Folge., vol. VI., p. 129. 



(5) N.J., 1882, vol. I., p. 163. 



