The chemical composition of the mineral Jamesonite is indicated by the formula Pb4FeSb6S14, a Lead Iron Antimony Sulfide. This Jamesonite belongs to the Sulfides and Sulfosalts mineral class. Mineral Jamesonite is most commonly used as mineral specimen and it is often found exhibiting nice and wonderful appearance when viewed under geological polarizing light microscopes. Jamesonite is one of the few sulfide minerals that form fine acicular crystals, which appear as hair-like fibers that are usually very interesting when viewed under petrographic polarizing light microscopes. It can be found that the fibers may appear so thick so as to cover a specimen with hair-like fibers when it is evaluated under polarizing microscopes. ??? It may also appear sparsely disseminated between other minerals and may be confused with actual hairs. There are other interesting minerals that also form similar acicular crystals that can be mistaken as Jamesonite. These are the mineral boulangerite and millerite. However, it has been also found that the crystals of mineral boulangerite are more flexible and millerite crystals are usually found colored yellow that is very interesting when viewed under polarized light microscope. Jamesonite is also sometimes confused with mineral Stibnite because it can be also found forming larger prismatic crystals just like stibnite. Jamesonite crystals are usually found brittle. Mineral Jamesonite belongs to the segment of Sulfides where antimony acts more like a metal than a non-metal and occupies the position where it is bonded to sulfurs. This segment is sulfosalts.
Mineral Jamesonite has been also called as gray antimony and feather ore. This Jamesonite mineral species was named after Robert Jameson (1774 ? 1854), of Edinburg. Jamesonite was first described at Cornwall, England in 1825.
Mineral Jamesonite crystals are often found dark gray in color that is more interesting when viewed under polarizing light microscopes. The luster that is commonly exhibited by mineral Jamesonite in reflected light of polarizing microscopes for geologists is usually metallic and silky. Mineral Jamesonite is commonly found having good cleavage in one direction perpendicular to its length, which can be found much clearly exhibited when the specimen is evaluated under geological polarizing light microscope. The fracture that is commonly found exhibited by mineral Jamesonite under polarizing microscope is usually uneven. The hardness measure of the Jamesonite when it is evaluated using the Mohs scale method is usually ranging from 2 to 3. When specimen of mineral Jamesonite is rubbed on a white porcelain streak plate, it is commonly found leaving a gray black streak. The specific gravity measure of the mineral is usually found ranging from 5.5 grams per cubic centimeters to 6.0 grams per cubic centimeters.
Mineral Jamesonite is known to crystallize in the monoclinic system, which can be seen clearly when specimen is evaluated with the aid of polarized light microscope for geologists. The monoclinic system of crystal formation comprises crystals having three axes of unequal lengths. Two of which are usually found in a position that is oblique or not perpendicular to one another. However, both of which are commonly found perpendicular to the third axis. Most crystals of mineral Jamesonite are found opaque in appearance. The crystal habit of mineral Jamesonite usually include dense or sparse felted masses of acicular crystals that are usually splendidly exhibited under polarizing microscopes. It can be also found having fibrous masses that are usually interesting when viewed under geological polarizing light microscopes. Sometimes, mineral Jamesonite is also found having radial crystals that radiate from a center without producing stellar forms and this is usually splendidly exhibited under polarizing microscope.
Jamesonite is a highly anisotropic mineral species. In fact it is strongly anisotropic when viewed under geological polarizing light microscopes. It appears alternately dark and illuminated when viewed between crossed nicols of petrographic polarizing light microscope. When viewed in reflected light of polarized light microscope, it usually appears gray black in color. It has also visible distinct pleochroism when evaluated under polarizing light microscopes. Mineral Jamesonite is commonly associated with other interesting minerals including arsenopyrite, pyrite, sphalerite, stibnite and galena. Jamesonite crystals are not flexible and they are usually found brittle. There is no specific data found on the toxicity and heath dangers for mineral Jamesonite. However, the specimen of this mineral species should be treated with great care and use of sensible precaution is advised upon handling them. Mineral Jamesonite is a non-radioactive mineral.
Jamesonite is actually a late stage hydrothermal mineral formed at moderate to low temperature. The best field indicators of mineral Jamesonite usually include luster, crystal habit, color, brittleness, and associations. Mineral Jamesonite notably occurs at several localities including Cornwall in England, some areas in the United States like South Dakota and Arkansas, Romania, Mexico and Zacatecas.