Till-: HKLATION OF MINERALS TO THE ELEMENTS 233 



monites, etc. Derived 



/S-H 

 from such acids as As ( S H 



\S-H 

 The group also includes basic, acid, nor- 



.-is proustitr, Ag.tAsS.-i. 

 m;tl, and meta groups. 



IV. Haloids, or salts derived from the haloid acids, as HC1, 

 1 1 Mr. Ill, and HF; halite, NaCl; iodyrite, Agl ; bromyrite, AgBr; 

 Huoritr, ( 1 aF 2 . 



V. Oxides, or the combinations of the elements with oxygen. 



a. The oxides of the univalent metals, as cuprite, Cu 2 O. 



b. Oxides of the bivalent metals, as zincite, ZnO. 



c. Oxides of the trivalent elements, as corundum, Al 2 O 3 . 



d. Oxides of the quadrivalent elements, as quartz, SiO 2 . 



Also included in this group are the hydroxides, in which the 

 base is combined with hydroxyl, as brucite, Mg(OH) 2 . 



The aluminites, ferrites, and chromites, salts of such acids 

 as HAlO 2 , as spinel, Mg(AlO 2 ) 2 , or of H(FeO 2 ), as magnetite, 

 Fe(FeO 2 )-2, and chromite, Fe(CrO 2 ) 2 , are included in this group, 

 though they must be considered as salts and not oxides. 



VI. Salts of the oxygen acids. 



a. Carbonates, H 2 CO 3 , as CaCO 3 , calcite; basic carbonates, 

 as malachite, (CuOH) 2 CO 3 , and hydrous carbonates, as 

 trona, Na^COs . 10 H 2 O. 

 6. Silicates, titanates, etc. 



Orthosilicates are the normal salts of the tetrabasic acid, H 4 SiO 4 , 

 as fayalite, Fe 2 SiO 4 . 



Metasilicates. Orthosilicic acid by a loss of some of its water 

 forms the dibasic acid, metasilicic acid. 



H-OV./O-;"H 



H 



-O\ a ./ 



-o/ Sl \: 



o-H 



There are many minerals which are salts of this acid, as enstatite, 

 MgSiO 3 , or leucite, KAl(SiO 3 ) 2 . 



Diorthosilicic acid is derived from two molecules of orthosilicic 

 acid by the loss of one molecule of water. 



H-0/ S \0-S""fi-6 1 , 



(HO) 3 =Si-0-Si=(OH) 3 ; 



It is an hexabasic acid, an example of which is barysilite, x 

 Pb 3 Si 2 O 7 . 



