OF CENTRAL CANADA PART II. 59 



^ ( (1) Streak, pale-brown. Colour, brown, black, yellow, &c. Mostly in in- 

 distinct crystals or small cleavable masses : Zinc Blende (No. 13). 

 (ra) Streak, dull or bright-red. Colour, brick-red. Magnetic after ig- 

 nition : Red Ochre and other varieties of Red Iron Ore (No. 20). 



j> (n) Streak, brownish-yellow. C., dark or light- brown. Magnetic after 

 iguition, and yielding water in the bulb.tube : Yellow Ochre and 



Brown or Bog Iron Ore (No. 34). 

 (o) Streak, pale-green ; colour, green : Malachite (No. 94). Some 



Chlorites (No. 80). 

 (p) Streak, pale-blue ; colour, blue. Mostly in crusts or earthy masses : 



Blue Carbonate of Copper (No. 95). Also Phosphate of Iron 



(No. 104.) 



SYSTEMATIC ARRANGEMENT OF MINERALS. 

 Mineral bodies are characterized partly by composition, and partly 

 by physical properties. Composition alone, is not sufficient in all 

 cases to define or individualize a mineral species, as certain substances 

 Carbon, for instance, in Graphite and the Diamond ; Carbonate of 

 Lime, in Calcite and and Arragonite may occur in nature under 

 two or more distinct physical conditions. On the other hand, a close 

 resemblance, in general aspect and other physical characters, may be 

 exhibited by minerals of very dissimilar composition. Minerals have 

 thus a double nature, so to say chemical and physical : the one 

 frequently in apparent opposition to the other ; and in this lies the 

 difficulty of framing a satisfactory classification of minerals. A 

 system of arrangement based on chemical composition, although un- 

 avoidably artificial in many of its details, is especially convenient for 

 practical reference, and on the whole is perhaps best suited to meet 

 the requirements of the general student. A system of this kind is 

 adopted, therefore, in the present work. It comprises five leading- 

 groups or classes. First, a group of simple or so-called Native Sub- 

 stances, as Native Sulphur, Native Gold, Native Silver, &c., the 

 naturally occurring elementary bodies of chemical language (See 

 under " Chemical Characters " in Part I). Secondly, a group of Sul- 

 phides and Arsenides, or compounds of sulphur, or of arsenic, with 

 various metals : galena, iron pyrites, arsenical pyrites, are examples. 

 Thirdly, a large group of oxygenized compounds, including Simple 

 Oxides, as red iron ore, &c., and various so-called oxygen-salts, as 

 Silicates, Carbonates, Sulphates, and the like. (See explanation of 

 Chemical Terms in Part I. Also the explanatory remarks prefixed 

 to the different groups and sub-divisions, in the following pages.) 



