Sulfides: Galena

Composition: PbS; bismuth and silver may substitute for lead

Crystal system: Isometric; commonly well crystallized or massive

7.6.1
galena crystals with dolomite
MO USA

Properties:

• Metallic lustre
• Lead-grey color
• Dark streak (lead-grey)
• Knife scratches very easily; fingernail barely scratches or not at all (Mohs Hardness 2.5)
• Very high density
• Three perfect cleavages mutually perpendicualr to each other
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Galena, the most common lead mineral, occurs with other sulfides in hydrothermal vein, replacement and massive sulfide ore deposits.

7.6.2
cleavable galena
Broken Hill NSW Australia

Galena is the most important source of lead, although cerussite and anglesite are locally important where ores containing galena or other lead minerals have been oxidized in the near surface environment. Lead mining and processing was an important historical polluter; however, most lead in the modern environment comes from the combustion of petrol (gasoline) and coal and the breakdown of old paints.