INDEX. 505 



Forms, primary,, divided into classes, 6 consist of the cube, 

 6 the regular tetrahedron, 6 regular octahedron, 7 

 rhombic dodecahedron, 7 octahedron with a square 

 base, 8 rectangular base, 8 rhombic base, 9 right 

 square prism, 9 right rectangular prism, 9 right 

 rhombic prism, 10 right oblique-angled prism, 10 

 oblique rhombic prism, 10 doubly oblique prism, 1 1 

 hexagonal prism, 11 rhomboid, 11 how distinguish- 

 ed by letters, 103 alphabetical arrangement of, 497 to 

 498 arranged according to classes, 498 to 501. 



Forms, secondary, defined, 11, 86 are simple or compound 

 86 produce new figures when they envelope the pri- 

 mary, 86 causes producing them not understood, 87 

 table of, 215. 



G 



Galena, see Lead, sulphuret. 



Goniometer, common, described^ 26 reflective, 27. 



H 



Haiiy's theory of crystals, 34 its disadvantages, 34. 

 Hemitrope crystals, 88. 



Indices, of secondary planes, 233. 

 Intersected crystals, 88. 



L 



Lead, sulphuret, its cleavage, 37. 



Lime, carbonate, its cleavage, 38 fluate, how it may be 



cleaved, 39. 

 Linneus gave the first descriptions of crystals, 33. 



M 



Mineral species defined, 6. 



Minerals, on the arrangement of, 439 primary forms of, 

 arranged alphabetically, 451 to 497 primary forms of, 

 arranged according to classes, 498 to 501. 



Modification of a crystal, the alteration of form occasioned 

 by secondary planes, 24 Comte de Bournon first des- 

 cribed crystals by their modifications, 34 the same 

 method adopted by Mr. Phillips, 34. 



Modifications, introduction to tables of, 95 are divided 

 into classes, 98 each class may consist of many indi- 

 vidual or particular modifications, 98 their differences 

 explained, 99 may produce new figures, 100 how 

 related to decrements, 253 to 282 of the cube, 107 

 3s 



