MINERALOGY ; WITH A CLASSIFICATION OF SILICATES. 37. 



long insisted. The relation of the specific gravity to the empirical erjuivalent weights of 

 minerals, must enter as an essential element into a classification which shall unite the 

 chemical and natural-historical systems. Similar isomeric relations exist between cyanite 

 and sillimauite (fibrolite), rutile and anatase, and, as I have elsewhere endeavoured to 

 show, among the carbon-spars. It becomes necessary in the study of mineral species to 

 determine their relative equivalent weights, to which specific gravity must be the chief 

 guide." 



§ 31. The relations of the members of the scapolite group' as a series parallel to tlie feld- 

 spars, already pointed out by the author in 1855, were not lost sight of, nor their connec- 

 tion with saussurite, but were the subject of a communication to the French Academy of 

 Sciences iu 1863, which was translated by the author and published at the time in the 

 American Journal of Science ~ as already noticed in § 10. In this paper, after recalling the 

 general argument so often set forth as to the princii^les of a new system of mineralogi- 

 cal classification, it was said " Meionite, with the oxygen ratios 3:2:1, is the most basic 

 term known of the series of the wernerites (scapolites). The proportion of silica in these 

 minerals augments until we reach in dipyre the ratios 6:2:1, with a density which does 

 not exceed 2.66. We might then expect to find a silicate which should be to dipyre what 

 zoisite or saussurite is to meionite, and Mr. Damour has recently had the good fortune to 

 meet with such a mineral in a specimen of jade from China, of which he has given us 

 the description and tlie analysis. {Comptes Rendus, May 4th, 1863.) This substance closely 

 resembles iu its physical and chemical characters the saussurite or jade from Monte E.osa, 

 of which it has the density, 3.34. It is a silicate of alumina, lime, and soda, and gives the 

 same empirical formula as dipyre. We may exj^ect to find between saussurite and this new 

 species, to which Damour gives the name of jadeite, other jades having formulas which 

 will correspond with the wernerites intermediate between meionite and dipyre. . . . 

 By its hardness, its specific gravity, and its indifference to acids, jadeite is completely 

 separated from the wernerite group, and takes its place alongside of zoisite or saussurite, 

 w^ith the garnets, idocrase, and epidotes." 



§ 32. To this last succeeded the paper of 186Y, on " The Objects and Methods of Minera- 

 logy," already noticed (§§12-14), in which was given a review of the subject as discussed 

 by me in various publications from 1853 up to that date. Before proceeding to show the 

 systematic application of the principles already set forth, it is proposed to consider further 

 the c[uestion of the relation between the atomic weights and densities, so often insisted 

 upon in the above publications. The study of the so-called ecjuivalent or atomic volumes 

 of solid and liquid species, got by dividing the assumed equivalent weight of these by 

 their specific gravities — water being taken as unity, — has occupied the attention of many 

 chemists since the early investigation of the subject by Le Royer and Dumas. The applica- 

 tion of this method to hydrocarbonaceous bodies, or to hydrated or double salts of admitted 

 high equivalent, is comparatively simple, but it becomes more difficult when we have to 

 deal with such compounds as mineral silicates, for which, as in the case of feldspars, micas, 



' The scapolites have very lately been taken up and discuased from the author'.^ pohit of view by Tschermak, 

 Monatshefte der Chemie, December, 1883, as will be noticed further on. The sliglit change in the empirical for- 

 mula of meionite suggested by Tschermak does not effect the present argument. 



-Compte Eendu de I'Acad., June 29, 1863, and Amer. Jour. Science, 1863, xxxvi. 42C-428, also the author's 

 C'liem. and Geol. Essays, p. 44G. 



