Jamesonite from Zacatecas, Mexico
(MM 6530)
Acicular, metallic crystals of Jamesonite on
a matrix of Quartz.
CHEMISTRY Pb4FeSb6S14
CRYSTALLOGRAPHY Monoclinic
CRYSTAL GROWTH AND HABITS Crystals are most commonly fibrous or acicular. Jamesonite often grows as felt-like masses. It can also occur as plumose or as massive growths.
COLOR AND OTHER OPTICAL PROPERTIES Black to gray, sometimes with an iridescent tarnish.
HARDNESS 2.5
SPECIFIC GRAVITY 5.6 - 5.7
LUSTER Metallic
STREAK Dark gray
BREAKABILITY Good cleavage on {001}; brittle
OCCURRENCE Jamesonite is formed during the later stages of low to moderate hydrothermal deposition of lead, silver and zinc deposition.
ASSOCIATED MINERALS Pyrite, Sphalerite, Galena, Tetrahedrite, Stibnite, Siderite.
MINERAL NAME Named after the Scottish mineralogist Robert Jameson.