412 DESCRIPTIVE MINERALOGY. 



I. 11. 



Oxide of zinc, 9fi.l0 95.00 



Oxide of iron, 2.90 4.50 



Carbon, 1.00 0.50 



It is, therefore, a nearly pure oxide of zinc. The above results agree very well with those 

 obtained from an examination of similar products in France. 



ORDER IV. LEAD. 



1. Galena. 



2. White Lead Ore. 



3. Anglesite. 



4. Yellow Lead Ore. 



5. Pyromorphite. 



6. Vauquclinite. 



Fig. 488. 



GALENA. 



[From the Latin galena, an ore of silver and lead.] 



Plomb Sulfure. Haiiij. — Sulphuret of Lead, or Galena. Ckavcland. — Sulpliuret of LeaJ. PhUlips and Thmnson. 

 — Hexahedral Galena, or Lead Glance. Jsmfsim. — Hexaedrischer Blei-GIanz. Mohs. — Galene. Bcudant. 



Description. Colour bluish grey, usually called lead-grey. Streak unaltered. It occurs 

 regularly crystallized ; also granular and massive, sometimes having a lamellar structure, and 

 at others almost compact. The primary form is a cube, Fig. 488. 

 Cleavage parallel with the primary planes, highly perfect, and easily 

 obtained. Fracture even, or flat conchoidal. Very frangible and sectile. 

 Lustre brilliant metallic. Opaque. Hardness from 2 . 5 to 3 . 0. Spe- 

 cific gravity from 7.40 to 7.65. Fusible before the blowpipe, with 

 the disengagement of fumes of sulphur. When heated on charcoal, 

 the metallic lead is obtained. Soluble in nitric acid, forming a white 

 precipitate of sulphate of lead. When dissolved in dilute nitric acid 

 with only a slight elevation of temperature, the solution produces a 

 precipitate of brilliant blades of lead upon a clean plate of zinc, but not upon a plate of cop- 

 per, unless it contains sulphuret of silver. 



Composition. Lead 85.13, sulphur 13.02 {Thomson). This is nearly in the ratio of 

 one atom of each of the constituents ; but it often contains small quantities of sulphuret of 

 silver. Formula PbS. 



V 

 V 



