XV.— GEOLOGY AND MINERALOGY. 121 



I.— Non-metallic minerals, placed on the left hand side of the 



room. 



11- — Metallic minerals, placed on the right hand side of the 

 room. 



NON-METALLIC MINERALS. 



The order of sequence into which the so-called rocks, or non- 

 metallic minerals are arranged, is as follows : 



Carbon class, including Diamond (see precious stones) Graphite 

 (Plumbago or black lead). Coal, Oil Shales, Amber, &c. 



Boron class, including Boron, &c. 



Sulphur class ; Ex. Sulphur found in volcanic districts. 



Alkaline and Earthy Minerals, divided into : 



1. Alkaline salts; Ex. Rock Salt, &c. 



2. Alkaline earthy salts; Ex. Calcite, Aragonite (Carbon- 

 ate of Lime, or Limestone), Selenite (Sulphate of Lime, or 

 Gypsum), Apatite (Phosphate of Lime), Fluor-Spar, &c. 



3. Alumina and Aluminates ; Ex. Corundum, including 

 Sapphire and Ruby (composed of alumina). Spinel Ruby 

 (an aluminate of magnesia), &c. Emery is impure corun- 

 dum mixed with oxide of iron. (See Catalogue pages 

 1 to 38, Nos. 1 to 433.) 



Silica and Hydrous Silica ; Ex. Quartz (including Rock 



Crystal, Amethyst, Agate, Flint, Jasper, &c.). Opal is hydrous 



silica, or silica containing water. (See Catalogue, pages 39 to 44, 

 Nos. 434 to 574.) 



Silicates proper, including the more important groups, namely : 



1. Pyroxene group ; Ex. Augite, &c., found in basalt and other 

 eruptive rocks. 



2. Amphibole group ; Ex. Hornblende, Asbestos, &c., occurring 

 chiefly in schists and eruptive rocks. 



3. Olivine group ; Ex. Olivine or Peridot, a bottle-green gem 

 found in basalt. 



4. Garnet group ; The red variety is a common gem. 



