A COMPARATIVE STUDY OF ETCH-FIGURES. THE 

 AMPHIBOLES AND PYROXENES. 



By R. a. Daly. 



Presented by J. E. Wolff, December 14, 1898. Received January 18, 1899. 



CONTENTS. 



PAGE 



Introduction 374 



Previous Notices of Etcli-Pits on Anipliiboles 374 



Reasons for the Present Investigation 375 



Terminology 375 



Discussion of Etch-Figures in the Microscope. Tlie Illustrations 37() 



Materials of Study • 378 



Methods used in the Investigation 381 



Advantage of using Cleavage Pieces 382 



Necessity of fixing the Conditions of Etching; Nature, Concentration, 



and Temperature of the Solvent 383 



The Optimum Exposure for the different Species in the Case of Hydroflu- 

 oric Acid 385 



Attackability of the different Species and of the different Faces on the same 



Species 386 



Description of the Etch-Figures 391 



Etch-Figures on (110) 391 



Actinolite Type 391 



Hornblende Type 394 



Wolfsberg Sub-type 394 



Krageru Sub-type 398 



Edenville Sub-type 399 



Philipstad Sub-type. Especial Anomalies in the Behavior of the 



Philipstad Hornblende 399 



Etch-Hills on Hornblende (110) 402 



Glaucophane Type 404 



Riebeckite Type 404 



Arfvedsoriite Type 404 



Etch-Figures on (010) 405 



Non-aluminous Aniphiboles. Experiments on the Dilution of the vSol- 



vent (Hydrofluoric Acid), and on its Mixture with Sulphuric Acid 405 



Aluminous Amphiboles 411 



Etch-Figures on Faces other than (110) and (010) 412 



The Orthopinacoid 413. 



