12 



MINERALS AND GEOLOGY 



this system. Prismatic Iron-pyrites, Mispickel or Arsenical-pyrites, 

 Native Sulphur, Topaz, Staurolite, Arragonite, Heavy spar, Celestine, 



Fia. 16. 



FIG. 17. 



FIG. 



Fia. 18. 



Fia. 19. 



FIG. 20. 



FIG. 21. 



and Epsom salt, are some of the principal minerals which belong to 

 the Rhombic group. 



The Monoclinic or Clino-Rhombic System. Rhombic prisms and 

 pyramids, and rectangular prisms and pyramids, with oblique or 

 sloping base, belong to this system. Figs. 22 to 24 are Monoclinic 

 combinations. Characteristic minerals comprise : Augite, Horn- 

 blende, Epidote, Sphene, Orthoclase or Potash Feldspar, Gypsum, 

 and Iron Vitriol or Sulphate of Iron. 



Fia. 22. 



Fia. 23. 



Fia. 24. 



FIG. 25. 



The Triclinic or Anorthic System The forms of this system are 

 oblique in two directions. The crystals in general are more or less 

 flat and unsym metrical in appearance, No two planes meet at right 

 angles ; and there are never more than two similar planes present in 

 any crystal belonging to the group. Axinite, Albite or Soda-Feld- 

 spar, and Sulphate of Copper, Fig. 25, are examples of Triclinic 

 minerals. 



