CLASSIFICATION. 91 



4. DESCRIPTIONS OF MINERALS. 



Classification. 



Some of the prominent points in the classification of minerals 

 adopted in the following pages are given in connection with the 

 remarks on chemical composition, pages 79. 



Many instructors in the science, and most of those who con- 

 sult a work on Mineralogy for practical purposes, prefer an ar- 

 rangement of the ores which groups them under the head of the 

 metal prominent in their constitution. The method of group- 

 ing mineral species according to the basic element has therefore 

 been here, to a large extent, followed. An exception has been 

 made in the case of the silicates, because it is with them almost 

 impracticable, on account of the number of basic elements they 

 often contain ; and, moreover, not more than half a dozen use- 

 ful ores exist among them. The silicates therefore, which in- 

 clude the larger part of all minerals, make together oiih of the 

 grand divisions in the classification, and they are presented ac- 

 cording to their natural groups, in the same order as in the 

 larger mineralogy. 



The prominent subdivisions in the classification are as fol- 

 lows : 



I. The Acidic division, including the acidic elements oc- 

 curring native, and the native compounds of the acidic elements 

 with one another. 



II. The Basic division, including the basic elements occur- 

 ring native, and the native binary and ternary compounds of 

 the basic elements — the silicates excepted. 



III. Silica and the Silicates. 



IV. The Hydrocarbon Compounds, including mineral oils, 

 resins, wax, and coals. 



The following are the chief subdivisions under these heads: 



I. Acidic Division. 



1. Sulphur Group. — The chief oxide a trioxide, its formula 

 R :J . includes Sulphur and sulphur oxides ; Tellurium and 

 tellurium oxides ; Molybdenum sulphide and oxide j Tungsten 

 oxide. 



