No. 5.] HARRINGTON — CANADIAN MINERALS. 305 



NOTES ON CHROME GARNET, PYRRHOTITE 

 AND TITANIFEROUS IRON ORE. 



By B. J. Harrington, B.A., Ph.D.* 



I. Chrome Garnet. 



Garnet affords us an excelleut example of the wide variatioa 

 in composition exhibited by many mineral species. The varia- 

 tion is due to what is known as isomorphous replacement, or the 

 replacement of one or more substances in a chemical compound 

 by analogous sub.stances without any essential change of form 

 resulting therefrom. 



If we take Rg R2 ^H ^12 ^^ ^^^ general formula for garnet, 

 the numerous analyses of the mineral which have been made 

 tell us that R may be represented by calcium, magnesium, iron 

 (in the ferrous state), manganese, &c., while R may be aluminium, 

 iron (in the ferric state), or chromium. With all these differ- 

 ences in composition, the crystals of the mineral are always 

 closely related or identical in form ; but, as might be expected, 

 the variations in specific gravity and colour are considerable. 



In a paper on "Apatite and its associated Minerals," which I 

 had the pleasure of reading before this Society about a year and 

 a half ago, garnet was mentioned as one of the rarer constituents 

 of the apatite bearing veins; and its occurrence was again noticed 

 in a report published by the Geological Survey last year. Of 

 the varieties which have been observed the most common is 

 probably a lime-alumina garnet; but the most interesting is a 

 beautiful emerald-green variety which was discovered some time 

 ago in the township of Wakefield, Quebec, and which has proved 

 on analysis to be cliromiferous. So far as I am aware there is 

 no instance recorded in which the element chromium has hitherto 

 been detected in any of the Laureutian minerals of Canada, 

 although it is well known to be a constituent of serpentines 

 and other minerals in succeeding formations. In order to ascer- 

 tain whether the Wakefield garnet resemb^'^d the original ouvaro- 

 vite or chrome-garnet, from Bissersk, io the Urals, a quantative 

 analysis has recently been made, and the results are given under 



* Read before the Natural History Society May 26th, 1880. 

 Vol. IX. T No. 5. 



