Jamesonite

Jamesonite is a sulfosalt mineral, a lead, iron, antimony sulfide with formula Pb₄FeSb₆S₁₄. With the addition of manganese it forms a series with benavidesite.[1] It is a dark grey metallic mineral which forms acicular prismatic monoclinic crystals. It is soft with a Mohs hardness of 2.5 and has a specific gravity of 5.5 - 5.6.[2] It is one of the few sulfide minerals to form fibrous or needle like crystals. It can also form large prismatic crystals similar to stibnite with which it can be associated. It is usually found in low to moderate temperature hydrothermal deposits.[1]

Jamesonite
Jamesonite crystals
General
Category	Sulfosalt
Formula (repeating unit)	Pb4FeSb6S14
Strunz classification	2.HB.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/a
Identification
Color	gray-black
Cleavage	{001} good; also possibly {010} and {120}
Mohs scale hardness	​2 1⁄2
Luster	metallic
Streak	gray-black
Diaphaneity	opaque
Specific gravity	5.63

It was named for Scottish mineralogist Robert Jameson (1774–1854). It was first identified in 1825 in Cornwall, England.[3] It is also reported from South Dakota and Arkansas, US; Zacatecas, Mexico; and Romania.