266 Warren— llmenite Rocks near St. Urhain, Quebec ; 



appearance a fine microperthite structure. If a polished sur- 

 face be immersed in cold dilute hydrochloric acid, the latter 

 very soon shows the characteristic color of ferric chloride, 

 becoming in the course of two or three hours quite strongly 

 colored. The solution gives reactions for ferric iron only. 

 Pure magnetite, similarly treated, dissolves somewhat more 

 readily, but the solution reacts strongly for both ferric and 

 ferrous iron. The steel-gray lamellae are deepened by the 

 action of the acid forming tiny grooves, indicating that it is 

 this part of the intergrowth that is dissolved. As will be seen 

 from the chemical analysis of the ore given later, the percent- 

 age of ferric oxide present is in general agreement with the 

 percentage of the steel-gray lamellae. These facts point 

 strongly to the conclusion that the latter are hematite in inti- 

 mate crystallographic intergrowth with ilmenite. It may also 

 be noted that the ilmenite grains are not affected by an ordi- 

 nary magnet, and indeed require a strong field on an electro- 

 magnet in order to be attracted to the point of picking up. 

 Their weak magnetic properties indicate quite clearly that 

 there is no magnetite present. The very fine powder rubbed 

 on smooth white paper gives a dull brownish black streak 

 (with perhaps a slight reddish tint) identical in appearance 

 with the streak similarly obtained from a mixture of f pure 

 magnetite (black streak) and J hematite (dark red streak). 



To the writer this intergrowth appears to have some interest 

 in connection with the composition of " titanic-irons" gener- 

 ally, and the disputed question of the isomorphism of hematite 

 and ilmenite. While it is impossible to make an exact estimate 

 of the amount of ferric oxide present as such in the inter- 

 growth, the approximate estimate given above agrees approx- 

 imately with the per cent of ferric oxide found by analysis. 

 From this it appears that the amount of Fe 2 3 mixed isomorph- 

 ously with the ilmenite must be small. The excess of Fe 2 3 so 

 commonly reported in ilmenite analyses has generally been 

 accepted to mean that the ilmenite and hematite molecules are 

 isomorphous. If the ilmenite grains in the present instance 

 possess the structure originally assumed by them on crystal- 

 lization from the magmatic condition, the idea at once presents 

 itself that the Fe 2 3 present in ilmenite may be always in large 

 part, at least, present in the form of a fine intergrowth, and 

 the desirability of examining carefully prepared polished and 

 etched specimens of ilmenite whose chemical composition is 

 accurately known is at once apparent. It is of course by no 

 means certain that the intergrowth is an original structure. 

 The two molecules may have crystallized originally as an iso- 

 morphous mixture and subsequently, under changed conditions 

 of temperature, etc., being no longer stable in the isomorphous 



