MINERALS OF OPHITES AND RELATED ROCKS. 5 



between which is that their constituents are quantitatively 

 varied : II. containing those in which the magnesia is variously 

 decreased by the introduction of other bases. 



Group I. comprises the following four sections : 



A, represented by typical serpentine, includes species or 

 varieties (retinalite, vorhauserite, bowenite, marmolite, thermo- 

 phyllite) in which the magnesia and silica stand to each other 

 in about equal proportions, and the water, from 11 to 14 per 

 cent., is pretty constant in quantity. 



B contains those in which the silica approaches to, or in a 

 few cases exceeds, 60 per cent., and the magnesia is reduced to 

 about 30. Aphrodite, sepiolite, and spadaite are examples. 



C comprises talc, steatite, pyrallolite, picrosmine, rensselaerite 

 (in general highly siliceous), with from 23 to 35 per cent, of 

 magnesia; but subhydrous, containing only from 3 to 7 per 

 cent, of water. 



D includes deweylite and cerolite, which are not much re- 

 moved from serpentine in the proportion of their base; but 

 they are superhydrous, holding somewhat over 20 per cent, of 

 water. 



In group II. a quantity of the magnesia is frequently more 

 or less replaced by alumina, oxide of iron, lime, and alkalies 

 (singly or associated), with variations in the amount of water, 

 giving rise to the following sections : 



A. Aluminous. Saponite, pyrosclerite, ripidolite, loganite, 

 leuchtenbergite, pseudophite. 



B. Ferruginous. Antigorite, villarsite, hydrophite, pseudo- 

 diallage (Heddle), monradite, bastite. 



C. Alumino -ferruginous. Penninite, prochlorite, tabergite, 

 corundophyllite, vaalite, neolite *, &c. 



D. Calcareous. Totaigite (Heddle). 



E. Alumino- calcareous. Chonicrite, seybertite, baltimorite 

 (Hauer). 



F. Alumino-calcareo-alkaline. Biharite, groppite. 



G. Alumino-chromiferous. Kammererite, rhodochrome. 

 H. Nickeliferous. Nouemite. 



I . Alumino-cupriferous. Venerite. 



Being essentially hydrous, it was to be expected that some of 



* Neolite, strictly speaking, is not an ophite-forming mineral but its con- 

 stituents relate it to serpentine, 



