60 THOMAS STEERY HUNT ON A NATURAL SYSTEM IN 



according to Tschermak (cajsi,,si,Joi., : that is to say, the ratio of al : si in the two 

 species remaining unchanged, there is an addition of an atom of ca,0|. But dipyre, which 

 was made the other term of the series, is no longer the most silicic scapolite. This, in 

 accordance with the former notation, would b'e 1 : 2 : 9, or, multiplying and correcting to 

 bring the formula into accordance with Tschermak's conclusion, 4 : 9 : 36. Eeverting to the 

 simplest atomic formulas, the two scapolites which form the extremes of our series difter 

 from anorthite and from albite in containing each one third of an atom additional of pro- 

 toxyd, being (caial3si4)oi2+ ^m,0| and (mial3si,o)o„., + -JmiO|. Multiplying by three, to com- 

 pare with the formiila given above for meionite, we haA'e, for this last and most silicic 

 scapolite, (m4al,,siv,)o,,, which represents the marialite of Pianura. described by Vou 

 Eath. 



§ *76. The scapolites however, contain more or less chlorine, as observed b}- Adams, 

 and by others. Found in small quantities in meionite, it equals in some examples 248 per 

 cent., though apparently absent in marialite. The theoretical chloriferous scapolite is, 

 however, according to Tschermak, a marialite in which, with the above formula, one atom 

 of oxygen is replaced by chlorine (4"20 per cent.), or in other words is albite (m,al.,siio)0|,-, 

 + |naicl„ the additional basic element being here chlorid instead of oxyd. In the 

 scapolites, as in the feldspars, in ascending the series, there appears a progressive increase 

 in alkalies, which gradually replace the lime, until in mizzonite and marialite we find con- 

 siderable soda and some potash. A general decrease in density is at the same time appa- 

 rent, but more accurate determinations of this factor are needed for the scapolites. We 

 have in the accompanying table revised the atomic formulas so as to correspond with the 

 ratio of 4 : 9 for protoxyds and alumina. 



The intermediate scapolites of the meionite-marialite series are imagined by 

 Tschermak to be, not as proposed by Yon Waltershausen and myself, crystalline intermix- 

 tures, but binary combinations in different proportions of the two silicates, meionite and 

 marialite. He notes (1) compounds holding one equivalent of marialite to two of meio- 

 nite, which are almost or completely soluble in acids ; (2) compounds with one of meionite 

 to two of marialite, incompletely soluble ; and (3) compounds with less than the latter 

 projîortion of marialite, insoluble in acids. This variation in solubility will in the chemist's 

 eyes, be, as already shown (§ 32), a reason for rejecting the notion that they are admixtures, 

 while he will at the same time repudiate the attempt to perpetuate in their formulas the 

 dualistic notions of a former day. These intermediate scapolites like the feldspars, labra- 

 dorite and oligoclase, and the various zeolites between thomsouite and stilbite, must 

 be regarded as distinct species. 



§ TT. In close relation to the scapolites comes a remarkable group comprising sodalite, 

 nosite and hauyne. Sodalite has the atomic formula of a chlorinated soda-meionite, being 

 (na^algsiijjooicli. Nosite is a similar species, in which the chlorine is replaced by oxy- 

 sulphion, while haiiyue is another species, in which the proportion of protoxyd base is 

 greater than in these, giving the ratio, 5 : 9 : 12. The relations of these various species to 

 anorthite and to each other, may, if anorthite be written (ca3algsiij)02„ be represented as 

 follows: meionite, (caaalgsij;,) 0^4 + caiOi ; sodalite, (na3al,|Si,2)o^,, + na,cl| ; nosite, (na3al,jsi,2)o24 

 + naiSjOj ; hauyne, (na3al,,si,o)o., + 2caiSi04. Both of these sulphatic species contain also 

 small amounts of chlorine. Ittnerite is a hydrous species related to these, but containing 

 a smaller proportion of sulphates than either, and, like the associated scolopsite, requires 



