APPENDIX 691 



pearance, and is used for the same purpose, as serpentine asbestos. 

 Hornblende is a constituent of some igneous rocks. 



Augite, a silicate of several elements. — The color is black or 

 dark green and the hardness about that of steel (H = 5-6). It usually 

 occurs in short, thick crystals. It is a rock-making mineral of wide 

 distribution and is an important constituent of " trap." 



Olivine (chrysolite, peridot), an iron magnesium silicate. — The 

 color is usually yellowish green, and the hardness that of quartz 

 (H = 6.5-7). It is an important constituent of some igneous rocks. 

 Large, clear crystals are cut for gem stones. 



Garnet, variable silicates of various bases. — The color is com- 

 monly red or black, but brown and green garnets also occur. The 

 hardness is that of quartz (H = 7). Garnets usually occur in crystals 

 with 12 similar faces (dodecahedrons or trapezohedrons) and are found 

 embedded in metamorphic rocks of various kinds. Garnets are crushed 

 and manufactured into sandpaper, and fine, clear specimens of good 

 color are cut for gem stones. 



