THM I'mv ii'\i. i;< K IOIIMIM; MIM.IIALS 615 



fractures common ; Krlirf m:irk.r.| ;in,| m lt r}, ; 



Colorless to green or brown; Interference eol-.r- 

 bright second or third orders; Parallel extinction; 

 Optically positive (+); p. 446. 



Pyroxenes; Monoclinic ; n= 1.68-1. 72; y a = 

 .022-.029. 



Prismatic crystals, grains or irregular outlines; Cleav- 

 age prismatic, 87 ; Color, shades of green, yellow, or 

 brown ; Relief strongly marked ; Interference colors 

 bright second order; Extinction from 36-54; Op- 

 tically positive (+) ; p. 419. 



Cyanite ; Triclinic ; n = 1 723 ; y - a = .012. 



In elongated crystals, columnar or tablets; Cleavage 

 distinct, 74 ; Colorless to bluish, when dark in color 

 pleochroic; Interference colors, gray to yellow or red 

 of the first order; Axial angle large; Optically nega- 

 tive (-). p. 461. 

 6. Pleochroic. 



Chlorite; Monoclinic; n == 1.576; -y - a = .001- 

 .013. 



Sheets or scaly aggregates ; Cleavage basal micaceous ; 

 Shades of green ; Relief not marked ; Pleochroism 

 marked ; Interference colors gray or yellow of the first 

 order, anomalously indigo blue ; Optically (i;) ; p. 497. 



Biotite ; Monoclinic ; n = 1.58 ; Y a = .085. 



Flakes, plates, or shreds; Micaceous cleavage well 

 developed ; Tabular sections show no cleavage and 

 have a very low relief ; Extinction nearly parallel ; 

 Pleochroism marked ; Interference colors bright second 

 order ; 2 V usually nearly zero ; Optically ( ) ; p. 492. 



Amphiboles; Monoclinic; n= 1.62-1.64; y a = 

 .016-.072. 



In crystalline outlines, irregular masses, or rounded 

 grains ; Cleavage prismatic, 124 30', well developed ; 

 Relief marked; Colorless, green or brown; Pleo- 

 chroism very marked in dark colored sections, 

 much less in colorless sections, absorption being the 

 greatest parallel to the cleavage cracks ; Interference 

 colors bright second order to high orders in basaltic 

 varieties; Extinction 9-20; Optically negative 



(-); P. 431. 



