OEIGIN OF CEYSTALLINE EOCKS. 



43 



oxygeu by fluorine. lu the second line, we find, besides monticellite and chrysolite 

 (including the pure magnesian variety forsterite or boltouite), the hydrous species, villar- 

 site. With these, moreover, belong the mauganesian species, tephroite ; the zincic, wille- 

 mite ; and the glucinic, phenacite. In the third line, the hydrous silicate, serpentine, with 

 the ratios, 4:3:2, stands alone. Serpentine, unlike villarsite, has no corresponding anhy- 

 drous magnesiau species, and it is worthy of note that, as Daubrée has shown, when dehy- 

 drated and fïised, it breaks up into chrysolite and eustatite, between which, excluding 

 water, it holds an intermediate position." Deweylite, in like manner, another hydrous 

 magnesian silicate with the ratios, 2:3:1, has no corresponding anhydrous species, but is 

 represented by the hydrous lime-silicate, gyrolite, the most basic of the pectolitic group as 

 yet known. 



TABLE OF PROTOXYD SILICVVTES. 



§ 84. We come next to the great section of bisilicates, represented among anhydrous 

 species by wollastonite, enstatite, pyroxene, many hornblendes, and the manganesian species 

 rhodonite, with many related species and sub-species. With these are the hydrous magne- 

 sian bisilicates, picrosmine, aphrodite, and cerolite, in which the oxygen-ratios, E : Si : H, 

 are respectively 1:2:|; 1:2: |; and 1 : 2 : 1|. These various bisilicates are represented 

 among the pectolitic group by plombierite and xonaltite ; the former a lime-silicate found by 

 Daubrée in the process of formation at the hot spring of Plombières in France, and having 

 the oxygen-ratio, 1:2:2. Of the less hydrated xonaltite, it is worthy of remark that, as 

 observed by Rammelsberg, it occurs in concentric layers with the anhydrous species, 

 rhodonite (bustamite), and the hydrous quadrisilicate, apophyllite. 



While many hornblendes have the ratio of a bisilicate, others are believed to have a 



'^ Compte Rendu de I'Acad. des Sciences, Ixii., le 19 mars, 1866. 



