XV. — GEOLOGY ANC MINERALOGY. 131 



Silver Glance (Argentite) is a very good example o mallea- 

 bility ; this mineral acts like lead when cut with a knife. 

 Flexibility and elasticity are well exemplified by Mica and 

 Flexible Sandstone. Of the latter two varieties are known one 

 from Brazil, the other from North Carolina. 



Another class of properties of minerals includes those which 

 fall under the sense of sight, as transparency, Ex.: Limpid Quartz • 

 translucency, Ex. : Cloudy Quartz. Lustre and colour are two 

 important characteristics by which many minerals can be known 

 at a glance. Lustre is either metallic, Ex. : Gold, Iron Pyrites ; 

 adamantine, Ex. : Diamond, Carbonate of Lead ; resinous 

 Ex. : Realgar ; silky, Ex. : Satin Spar ; or vitreous, Ex. : 

 Quartz. Minerals which exhibit metallic or adamantine lustre 

 are, in general, heavy. There are some minerals of which the 

 colour is characteristic, Ex. : Malachite, green. There are 

 others which occur of different colours, Ex. : Corundum, red 

 (Ruby), blue (Sapphire), green (Oriental emerald), purple 

 (Oriental amethyst). 



VL— COLLECTION ILLUSTRATING DETERMINATION 



OF MINERALS. 



Under this title is a collection, the object of which is to 

 illustrate some simple processes of testing, by exhibiting the most 

 common minerals which answer to the tests. 



First of all a ready distinction is made between minerals 

 possessing, or not possessing a metallic lustre. Hence two 

 classes. The minerals exhibiting a metallic lustre are divided 

 into two groups according to their resistance and fusibility under 

 the blowpipe. The first group includes minerals which are easily 

 fusible or volatile, and leads to minor subdivisions, the principal 

 of which are characterised by the presence or absence of sulphur 

 antimony, arsenic or tellurium, as shown by a careful use of 

 the blowpipe. A great number of well-known ores are identified 

 by these tests. The second group includes minerals which are 

 infusible, or fuse with difficulty and give a magnetic mass after 

 being heated under the blowpipe. It includes several ores of 

 iron, chrome, &c. 



