Jamesonite is a lead iron antimony
sulphide mineral of the formula Pb4
Synonyms: feather ore and grey antimony
Colour: Dark lead grey
Lustre: Metallic and silky
Crystal System: Monoclinic
Cleavage: Good basal cleavage (perpendicular to length of crystals)
Streak: Dark grey/black
Include Cu, Zn, Ag and Bi.
Jamesonite is formed by hydrothermal fluids and often occurs in veins with other antimony sulphides and lead/silver or copper rich antimony sulphides. A good example of such an occurance is in Cornwall, England, where it was first discovered in 1825. Other locations include South Dakota and Arkansas, USA; Zacatecas, Mexico and Rumania. It is not a common mineral.
Jamesonite is usually identified by its acicular (needle-like) crystals, which are generally smaller and more brittle than those of stibnite, with less definition. It can be differentiated from galena by colour as it is a darker grey. Boulangerite can be confused with jamesonite at first glance, but its flexible crystals give it away. Another sulphide, millerite, also forms similar acicular crystals, but is identified by its yellow colour.
Problems in mining:
As a sulphide mineral, jamesonite is often found in association with pyrite, marcasite and pyrrhotite. Acid mine drainage, which is caused by the spontaneous decomposition of such minerals, often occurs in sulphide mines. The products of this breakdown are highly soluble in water, and cause it to become acidic, with a pH of 1.5 to 3.5. This is a major environmental problem caused by mining. This means that great care must be taken when mining jamesonite and other metal sulphides, which increases the cost of mining such minerals.
Jones, A.P., 2000. Collins Wild Guide: Rocks and Minerals. Harper Collins Publishers Ltd., London.