44 ON THE POSITION OF LIEVRITE 



Other words, they fail to present any satisfactory indication of the place 

 which the Licvrite should occupy amongst the Silicates generally. 

 Reflecting upon this, it occurred to me that the true composition of the 

 mineral might be arrived at by tracing out its mineralogical affinities. 

 If this seem paradoxical, it must be remembered that purely mineralo- 

 gical considerations have taken the initiative on more than one occasion 

 in the solution of obscure questions connected with mineral chemistry. 

 "Whilst, for example, the various garnets, the diff'erent varieties of 

 pyroxene, &c., were still kept apart by the chemist who adhered to 

 chemistry alone. Mineralogy insisted upon their union, and thus led 

 the way to the recognition of Isomorphism. If the relationship of 

 Lievrite to a mineral of known composition can be clearly shown, a 

 great assistance will at least be afforded towards the deduction of its 

 true atomic character. 



On comparing this mineral with other silicates, one cannot help being 

 struck by the remarkable correspondence existing between it and 

 Chrysolite — at least, as regards the so-called Fayalite and other iron- 

 holding varieties of the latter. It is curious that this coincidence 

 should hitherto have escaped attention. The gelatinization of the 

 silica in acids, a very peculiar character in the case of anhydrous 

 silicates, is exhibited by the two species in common. Their condi- 

 tions of occurrence are also more or less identical, the form in each is 

 Trimetric with axial relations in part corresponding, and each contains 

 an unusually low average of silica. This amounts, in Hyalosiderite 

 and Fayalite, to about 30 per cent. The same also in Lievrite. Dana 

 places the latter mineral (though doubtfully) in his Andalusitb 

 Oroup, with Andalusite, Topaz, and Sfaurolite ; but a collocation of 

 this kind is an exceedingly forced one. Geological relations (an 

 element in Mineralogical Classification of the highest importance, al- 

 though hitherto strangely overlooked), composition, and general cha- 

 racters, are all opposed to it. The form, it is true, is Trimetric, with 

 some remote analogy, as shewn by Dana, to that of Andalusite ; but 

 since we find such opposite minerals as Aiigite and Borax, for ex- 

 ample, exhibiting an identity of crystallization, no great stress can be 

 placed on this character. There is an equal amount of crystallo- 

 graphic correspondence, moreover, between Lievrite and Chrysolite, 

 whilst in other respects the two present a close agreement. In 

 Chrysolite, several vertical prisms are known (the ooP series of Nau- 

 mann and most German crystallographers ; / series of Dana ; V series 



