INDEX. 507 



Ociahedron witb a square base, defined, 8 its axis, 13 



its modifications, 126. 

 Octahedron with a rectangular base, defined, 8 its axis, 13 



its modifications, 138. 

 Octahedron with a rhombic base, defined, 9 its axis, 13 



its modifications, 146. 



P 



Parallellogram, defined, 5. 



Parallelopiped, defined, 5. 



Planes of crystals, natural, defined. 1 cleavage, 1 termi- 

 nal, 3 lateral, 3 similar, 3 tangent, 24. 



Position of crystals, 17. 



Primary form, see Form, primary. 



Prism, defined, 9 right, 9 oblique, 9. 



Prism, right square, defined, 9 its axis, 14 -its modifica- 

 tions, 162. 



Prism, right rectangular, defined, 9 its axis, 14 its modi- 

 fications, 166. 



Prism, right rhombic, defined, 10 its axis, 15 its modifi- 

 cations, 170. 



Prism, right oblique-angled, defined, 10 its axis, 15 its 

 modifications, 176. 



Prism, oblique rhombic, defined, 10 its axis, 15 its mo- 

 difications, 180. 



Prism, doubly oblique, defined, 11 its axis, 16 its modi- 

 fications, 190. 



Prism, hexagonal, regular, defined, 11 its axis, 16 its 

 molecule a triangular prism, 30 its modifications, 196. 



Projection, orthographic, explained, 403. 



Pseudomorphous crystals, 93* 



Pyro-electricity, 76 sometimes influences the modifications 

 of crystals, 76. 



R 



Rectangle, defined, 4. 



Rhomb, defined, 4. 



Rhombic dodecahedron, see Dodecahedron, rhombic. 



Rhomboid, defined, 11 how produced by cleavage from 

 the hexagonal prism of carbonate of lime, 80 its mo- 

 difications, 200. 



Rome de L'Isle produced the first rudiments of crystallo- 

 graphy, 33. 



