PHYSIOGRAPHY. 



Stilbite. 



209 



STILBITE. Prismatoidal Kouphone Spar. 

 MOHS. 



Primary form. Right rectangular prism. 

 Secondary form. 



Fig. 420. 



Faroe. 



M on a' 120 30' PHILLIPS. 



a on a 1 118 50 " 



M on d 133 30 " 



Cleavage, parallel to M and T, the former of which, on- 

 ly is perfect. Fracture uneven. Surface P often curved, 

 M vertically streaked, T still more so. 



Lustre vitreous. The faces M, both as faces of crys- 

 tallization and of cleavage, exhibit a perfect pearly lus- 

 tre. Color white prevalent, various shades of yellow, red 

 and brown. Streak white. Semi-transparent . . . translu- 

 cent. 



Brittle. Hardness = 3-5 . . . 4-0. Sp. gr. =2-161, 

 white crystals from Iceland. 



Compound Varieties. Twin-crystals which assume a 

 cruciform aspect, but rare. The crystals are frequently 

 aggregated in the form of a sheaf. Implanted globules, sur- 

 face very drusy, composition, imperfectly columnar, and 



18* 



