MINEEALOGY. 



81 



These are succeeded by a third section of this division, namely, by 

 minerals to form which compounds belonging to each of the former 

 sections are combined together. 



These three sections may be severally represented by their promi- 

 nent members, the arsenides, the sulphides, and the arseno-sulphides. 



Besides the three sections already mentioned, this division contains 

 a fourth, wherein metallic sulphides are so combined with sulphides 

 of Arsenic, Tin, Iron, &c, as to produce a series of sulphur salts, 

 in the constitution of which Sulphur plays the part which Oxygen 

 plays in the ordinary oxygen-salts, 

 ctioni., The first of these sections comprises the cuprous arsenides, such Cases 

 •senides', as Domeykite, the tricuprous arsenide ; also, the antimonide of 4< 

 Silver or Dyscrasite, diargentous antimonide. Besides these there 

 are included in this section several compounds of Iron, Cobalt, and 

 Nickel. Nickeline, called also " Copper Nickel," from its colour, 

 is a rhombohedral mineral, the nickel arsenide. Chloanthite is 

 the nickel diarsenide and Smaltine, or " tin-white Cobalt," the 

 cobalt diarsenide, of which Safflorite is a variety containing Iron in 

 place of a part of its Cobalt. These minerals are cubic in crystal- 

 lisation, but some of the same substances which constitute them are 

 also found in orthorhombic forms, affording examples of dimorphism. 

 Thus the nickel diarsenide, when thus occurring in crystals of the 

 orthorhombic system, is the mineral Chloanthite, and Leucopyrite is 

 a corresponding iron diarsenide. In this section is also included the 

 cobalt triarsenide, Skutterudite. 



The second section includes the various compounds of Sulphur, 

 Selenium, or Tellurium — the Thionid elements — with the metals. 

 Silver, a monad element, and Copper, a metal that in one group of its 

 salts plays the part of a monad element, contribute to form a small 

 group in this section of the type M 2 2. Eucairite is a selenide of Silver 

 and Copper, and Crookesite is a selenide of Copper and Thallium. 

 Hessite is a telluride of Silver, Naumannite the corresponding 

 selenide of Silver, while Argentite is the sulphide of Silver. The 

 latter are cubic in crystallisation, but the silver sulphide is a dimor- 

 phous mineral presenting itself as Akanthite in forms belonging 

 to the orthorhombic system. To this system belongs also Copper- 

 glance, a valuable ore of Copper, the " cuprous " sulphide. Among the 

 other important minerals in this section, a cubic series of mono- 

 sulphides occurs which includes two commercially very important 

 ores — Galena, the sulphide of lead, and Blende, the sulphide of zinc. 



A Rhombohedral series includes Covelline, the cupric sulphide, Cases 

 Cinnabar, or mercuric sulphide, the unique ore of the important metal 5 & 6. 

 Mercury. Millerite is the nickel monosulphide, and Greenockite, a 

 rare mineral in bright yellow crystals, consists of the corresponding 

 cadmium sulphide. 



There is also an important series of disulphides wherein Hauerite 

 and Iron-pyrites, which are respectively the persulphide of manga- 

 nese and of iron, are cubic, while as Marcasite the latter com- 

 pound is orthorhombic in crystallisation. These two forms of iron 



