XX If COXTKNTS. 



{SECTION II. 



The Natural- Historical Properties of Compound Minerah. 



. 178. Regular and Irregular Composition . 242 



. 179- Regular Composition. Twin-crystals . 243 

 . 180. Irregular Composition. Groupe and Geode of 



Crystals . . . 252 



. 181. Imitative Shapes . . 253 

 . 182. Imitative Shapes, originating in the Groupes of 



Crystals . . . 253 

 . 183. Imitative Shapes arising out of the Geodes of 



Crystals ... 254 



. 184. Amorphous Compositions . . 257 



. 185. Accidental Imitative Shapes . 258 

 . 186. Regular accidental Imitative Shapes. Pseudo- 



morphoses . . . 259 



. 187. Irregular accidental Imitative Shapes . 263 



.188. Particles of Composition . . 265 



. 189. Single and Multiple Composition . 268 



. 190. Characteristic Marks of Composition . 269 



. 191. Structure of Compound Minerals . 272 



. 192. Composition is of little value in Natural History 273 



SECTION III. 



The Natural-Historical Properties common to loth Simple and Com- 

 pound Minerals. 



. 193. Division . . .276 



CHAPTER I. 



Of the Optical Properties of Mineral*. 



. 194. Explanation . . .276 



. 195. Lustre, Colour, Transparency . . 277 



. 196. Kind and Intensity of Lustre . 278 



. 197. Series in the Differences of Lustre . 281 



. 198. Colour, properly so called, and Streak . 282 



. 199. Division of Colours f . 282 



