XVIL] CONSTITUTION AND VOLUME OF MINERAL SPECIES. 445 



in the American Journal of Science for March, 1864 (Vol. 

 XXV. page 258), where the family of the feldspathides is 

 made to include the scapolites or wernerites, and also beryl and 

 iolite, which have a similar equivalent volume. The former 

 is a glucinic feldspathide, subject, like the feldspars proper, 

 leucite, and the scapolites, to kaolinization ; while iolite is a 

 magnesic feldspathide, having the oxygen ratios 5:3:1, cor- 

 responding to barsowite and bytownite, and intermediate be- 

 tween labradorite and anorthite. 



[The relations of the feldspathides to the grenatides (in which 

 are included the garnets, idocrase, epidote, and zoisite) fur- 

 nish an important illustration of the notions put forward in 

 the preceding pages. In the American Journal of Science for 

 1859 (XXVII. 336) will be found a memoir on Euphotide and 

 Saussurite, in which I showed that the saussurite of Monte 

 Eosa (the jade of De Saussure) does not belong, as previously 

 supposed, to the feldspathides, but from its chemical and physi- 

 cal characters is to be regarded as a zoisite. This substance, 

 which is very distinct, alike from the compact feldspars with 

 which it had been confounded, and from the compact amphibole 

 to which also the name of jade is sometimes given, has a specific 

 gravity of 3.35 and a hardness of 7.0. It is only attacked 

 by acids after intense ignition or fusion, by which it is con- 

 verted into a soft glass having a specific gravity of 2.80. By 

 analysis it is found to have the composition of zoisite or of 

 meionite, these two species having the same centesimal com- 

 position. It has, however, the characters of the former, and 

 differs widely from meionite, which is a scapolite having a 

 specific gravity of 2.70 and a hardness of 5.5, and is readily 

 attacked and decomposed by acids. 



[The Comptes Eendus of the French Academy of Science 

 for June 29, 1863, contains a communication from me, which 

 is translated in the American Journal of Science for November, 

 1863 (page 427). In this, after giving in brief the history of 

 euphotide and saussurite and the results of my examinations, I 

 said as follows, referring to the memoir of 1859 : 



"In the memoir from which the foregoing results are cited 



