MINERALOGY. 



79 



(ii.) Elements of the Sulphur group (the Thionids, 

 viz., Tellurium, Selenium and Sulphur). Cases 

 3d to 6g. 



(iii.) and (iv.) Elements of both the Arsenic and Sul- 

 phur groups. Cases 6h to Sf. 



Division III. The Compounds of Metals with elements of the Chlo- 

 rine Group (the Halogen elements — Iodine, Bromine, 

 Chlorine and Fluorine). Cases 8g to 9d. 



Division IV. Compounds of elements with Oxygen. Cases 10a to 

 40h. 



Division V. Organic Compounds. Case 41. 



These Divisions are again subdivided into sections and classes, the 

 latter embracing the minerals which fall under the same general 

 chemical denomination; as, for instance, the salts of the same acid or of 

 a group of acids chemically and crystallographically equivalent to each 

 other. Each class is further separated into distinct chemical series, 

 the minerals included in any series being such as are designated by 

 the same or equivalent typical formulae. Subordinated to this chemical 

 systemof classification is the final distribution of the several homotypical 

 species of each chemical series, into distinct crystallographic series, 

 arranged according to the crystalline system to which they belong ; the 

 order of sequence of these systems being — 1 st, the Cubic System ; 2nd, 

 the Tetragonal or Pyramidal System; 3rd, the Orthosymmetric *or 

 Orthorhombic System; 4th, the Hexagonal or Rhombohedral System; 

 5th, the Monosymmetric or Oblique System ; 6th, the Asymmetric or 

 Anorthic System; and finally, Amorphous substances, that either pre- 

 sent no crystalline forms, or the forms of which, if they be crystal- 

 line, are not determinable. In the following observations the term 

 *■ group" will be reserved to connect Minerals, whether individual 

 species, series, or classes, which present such a community of physical 

 and other characters as imparts to them a sort of family resemblance. 



Division I. The Native Elements, 



In the first two cases are arranged such of the elementary forms of 

 matter as are found occurring in nature in the uncombined state. 

 These native elements, which form but a small proportion of those 

 the chemist has eliminated from the Mineral Kingdom, are arranged in 

 sections, of which the first is that of the native metals and their 

 alloys.. 



Of the series of native metals crystallising in the cubic sj^stem the Cafes 

 various forms of Copper, Silver, and Gold are the mostimportant ; and 1 & 2. 

 crystals of these metals are exhibited, remarkable for the perfection of 

 their forms, or conspicuous for their size. The crystallised copper from 



