ART. 2 PROPEETIES OP GLAUCONITE KOSS 15 



The proportion of alkalis is remarkably constant, and there is clearly no evi- 

 dence of the substitution of these by water, or, as was assumed by Clarke, by the 

 magnesia group. There is, however, considerable replacement of potash by 

 soda, * * * ^ and it may be suggested that the name "soda-glauconite" 

 should be used to distinguish these varieties. 



In the groups R2O3 and RO the molecular proportions are not constant and 

 do not stand in any simple ratio to the silica and alkalis; the ordinary substitu- 

 tions of alumina for ferric iron and magnesia for ferrous iron are therefore insuflS- 

 cient to explain the analyses. If, however, the (Fe, Mg)0 and (Fe, Al)203 are 

 treated as mutually replaceable, considerable improvement can be brought 

 about. The total for these two groups combined is given in the last column of 

 Table II, and it will be seen that, with the exception of Nos. 4, 6, and 7, the total 

 is constant and in simple ratio to the silica. The ratios so obtained lead to the 

 simple formula 



R20.4(R203, RO).10SiO2.nH2O, 



the ratio of bases to silica being 1 : 2. 



There exists a certain justification for regarding the above substitution as 

 possible, for the only definite hydrate of Fe203 known to exist is the monohy- 

 drate, which may be written OFeOFe(OH)2 resembling Fe(0H)2. The extent 

 of this substitution is not great, the ratio of R2O3 to RO lying between the limits 

 3 : 1 and 1 : 1. 



As regards the water, apart from the observation that it does not substitute 

 the solid constituents, there is no information as to the extent to which it is 

 present in definite combination ; detailed work on the dehydration would be 

 necessary to throw light on this question, and it has been thought best to 

 omit this from the present paper. 



The writer is in substantial agreement with Hallimond as to the 

 chemical composition of glauconite. In fact, most of the present 

 paper was prepared before the publication of Hallimond's paper, 

 and so we have come independently to substantially similar con- 

 clusions. 



CELADONITE 



Only a few analyses of celadonite are available and the mineral 

 appears to be even more difficult to obtain in the pure state than 

 glauconite. For these reasons no trustworthy interpretation of the 

 chemical relations of celadonite can be attempted at the present 

 time. If the analyses are plotted they all seem to fall near the 

 composition curves of glauconite when extended far to the left in 

 Figure 1. Therefore celadonite may possibly be made up of the 

 same or a closely related chemical series. 



Celadonite of unusual purity has been collected in Cuba by Hewett 

 and kindly placed at the disposal of the writer for examination. 

 This material has indices of refraction that are nearly the same as 

 those of glauconite, but the habit is fibrous, rather than micaceous 

 as in glauconite. The optical character is very difficult to determine 

 as the acute bisectrix is parallel to the thin fibers, but it is prob- 

 ably (-[-) rather than ( — ) as in glauconite. This indicates that 

 celadonite may be distinct from glauconite although it is closely re- 

 lated to it in chemical composition. 



o 



