DALY. • — ETCH-FIGURES ON AMPHIBOLES, 429 



nous amphiboles, signalized by the two-group division of all our hand- 

 books, is once more confirmed. At the same time, attention has been 

 again called to the overwhelming importance of a sesquioxide, whether 

 iron oxide or alumina, in the mineral. 



Glaucophane and gastaldite are the same species, and both isomorphous 

 with hornblende.* 



Arfvedsonite appears to hold a more or less independent place in the 

 family of amphiboles. ' 



Barkevikite is more closely related to common hornblende than to 

 arfvedsonite.f 



Anthophyllite and gedrite are plainly orthorhombic and holohedral. 



Aenigmatite diverges considerably from the amphibole habit, but be- 

 trays a tendency toward symmetrical cohesional property, as it does 

 toward crystallographic symmetry. t 



Lastly, it is believed that our present methods of determination of 

 species can be reinforced by the detailed study of mineral groups with 

 respect to etching. The peculiarities of the pits on the cleavages of 

 riebeckite, arfvedsonite, and barkevikite make it easy to say to which 

 of these a given cleavage flake belongs. Similarly, the differentiation 

 of crossite and glaucophane, difficult as it often is by purely optical 

 methods, is ready at hand if the mineral be etched on (110). The 

 striking characteristics of the Philipstad hornblende (V. 101) first became 

 evident in the process of etching cleavage pieces. Its description as a 

 new variety will form the sequel to this paper. 



* Cf. Striiver's statement: "It is probable that glaucophane and gastaldite 

 are isomorphous with amphibole [proper], but it is not yet proved." Neues Jahrb. 

 fiir Min., etc., 1887, Bd. I. p. 217. 



t The same opinion is held by Lacroix, chiefly on optical grounds (Mine'ralo- 

 gie de la France, Tom. I. p. 561) ; the opposite opinion by Brogger (Zeit. fiir Kryst., 

 Bd. XVI. p. 414), followed by Dana (System, p. 403), and Hintze (Handbuch. 

 p. 1256). 



f See Brogger, op. cit., p. 424. 



