THE GEOLOGIST. 



earthy matter : in tlie impure varieties the quantity of iron, lime, and 

 alumina amounts, at times, to as much as 37 per cent. But Carbon 

 is most important as the foimdation of the Coal family, divided into 

 tlu'ee species,— ^n^AraczVc, Common-coal, and Brown-coal or Lignite : 

 these, however, are more rocks than minerals, and will be described 

 as such. The bituminous variety of carbon, formed by its combi- 

 nation with hydrogen, is classed separately as 



2. BiTTTMEif ; Naphtha; Petroleum; Asphaltum. Contains about 12 per 



cent, of hydi'ogen. Naphtha, the purest variety, is liquid ; it becomes 

 thick by exposure, and is converted into Petrolemn. Asphaltum is 

 the solid variety. ' • 



3. Sulphur. 



4. W ATER ; Ice ; Firn or Nevee. fl. 



5. Corundum ; Emery. Al. The gi'anular and massive variety is Emery. 



The opaque crystalhne variety is Corundum ; the transparent crys- 

 talline blue and red varieties are respectively Sapphire and Ruby. 



6. Quartz ; Jasper, Hornstone or Chert. Si. One of the most abundant 



minerals m nature. The pure transparent variety is RocTc-crystal, and 

 the blue and yellow Amethyst and Topaz. Jasper is the variety 

 variously coloured by the oxides of iron principally. Hornstone or 

 Chert are names given to compact quartz substances. 



7. Opal ; Chalcedony ; Flint. Si + H. Compact or uncleavable quartz. 



Silica with 5 to 12 per cent, of water. Hyalite is the glassy trans- 

 parent "wariety, and there are various coloured ones. The siliceous 

 deposits from geysers and other hot springs are of this mineral. Opal 

 difiers fi'om quartz, besides its containing water, by its much lower 

 specific gTavity, inferior hardness, simple refraction, and other chemical 

 chai-acters. Chalcedony and Flint are usually classed as anhydrous 

 silica, but Fuchs considers them to be a mixture of quartz and opal. 

 He consequently divides compact quartz into two kinds : the one 

 containing opal, hke chalcedony and flint ; and the other free from 

 opal, like chert. Bischof considers rock-crystal and opal as the final 

 members of a series of sihceous minerals ; the former perfectly crys- 

 tallized, the latter perfectly amorphous. 



8. HE]\rATiTE, Specidar-iron. Fe. The crystalline variety with metalhc 



lustre is usually called specular-iron {Fer oligiste). It is an 

 abundant form of iron, and has many sub-varieties passing mto each 

 other. 



9. Browx Hematite, Limnite; Goethite ; with many sub-varieties. 



'Fq, + il. Hydrous per-oxide of hou. Limnite and Goethite ai-e 

 strictly different minerals, the former containing 14, and the latter 10 

 l>er cent, of water. 



10. jNIagnetite, Magnetic Iron. A combination of 1 atom of per-oxide 



