Franckeite, chemical formula Pb₅Sn₃Sb₂S₁₄, belongs to a family of complex sulfide minerals. Franckeite is a sulfosalt. It is closely related to cylindrite.

Franckeite
Franckeite var. Potosíite, San José Mine, Cercado Province Bolivia. Field of view about 10 mm.
General
Category	Sulfosalt mineral
Formula (repeating unit)	(Pb,Sn2+)6Fe2+Sn2Sb2S14
IMA symbol	Fke[1]
Strunz classification	2.HF.25b
Dana classification	03.01.04.02
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	Grayish black
Crystal habit	Typically in spherical, rosette aggregates of thin plates; commonly massive, radiated, or foliated
Twinning	Complex
Cleavage	{010}, perfect
Tenacity	Flexible, inelastic; slightly malleable
Mohs scale hardness	2.5 – 3
Luster	Metallic
Streak	Grayish black
Diaphaneity	Opaque
Specific gravity	5.88 – 5.92
Pleochroism	Weak
References	[2][3][4]

It was first described in 1893 for an occurrence in Chocaya, Potosí Department, Bolivia. It is named after the mining engineers, Carl and Ernest Francke.^[3] It can be found in Bolivia at Poopó in Oruro and at Las Aminas, southeast of Chocaya, in Potosi. Franckeite has an average density of 5.7 and can be both grayish black, blackish gray in color.

It occurs in hydrothermal silver-tin deposits in Bolivia and in contact metamorphosed limestone deposit in the Kalkar quarry in California. It occurs with cylindrite, teallite, plagionite, zinkenite, cassiterite, wurtzite, pyrrhotite, marcasite, arsenopyrite, galena, pyrite, sphalerite, siderite and stannite.^[2]