Kesterite

Kësterite is a sulfide mineral with a chemical formula of Cu₂(Zn,Fe)SnS₄. In its lattice structure, zinc and iron atoms share the same lattice sites. Kesterite is the Zn-rich variety whereas the Zn-poor form is called ferrokesterite or stannite. Owing to their similarity, kesterite is sometimes called isostannite.^[5] The synthetic form of kesterite is abbreviated as CZTS (from copper zinc tin sulfide). The name kesterite is sometimes extended to include this synthetic material and also CZTSe, which contains selenium instead of sulfur.^[6][7]

Kësterite
General
Category	Sulfide mineral
Formula	Cu2(Zn,Fe)SnS4
IMA symbol	Kës[1]
Strunz classification	2.CB.15a
Crystal system	Tetragonal
Crystal class	Disphenoidal (4) H-M symbol: (4)
Space group	I4
Unit cell	a = 5.427, c = 10.871 [Å]; Z = 2
Identification
Color	Greenish black
Crystal habit	Massive, pseudocubic
Cleavage	None
Mohs scale hardness	4.5
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	4.54–4.59 (meas.); 4.524 (calc.)
References	[2][3][4]

Occurrence

Kesterite was first described in 1958 in regard to an occurrence in the Kester deposit (and the associated locality) in Ynnakh Mountain, Yana basin, Yakutia, Russia, where it was discovered.^[2][3][4]

It is usually found in quartz-sulfide hydrothermal veins associated with tin ore deposits.^[2] Associated minerals include arsenopyrite, stannoidite, chalcopyrite, chalcocite, sphalerite and tennantite.^[4]

Stannite and kesterite occur together in the Ivigtut cryolite deposit of South Greenland. Solid solutions form between Cu₂FeSnS₄ and Cu₂ZnSnS₄ at temperatures above 680 °C. This accounts for the exsolved kesterite in stannite found in the cryolite.^[8]

Kesterite structure. Orange: Cu, blue: Sn, grey: Zn/Fe, yellow: S

Use

Kesterite-like substances are being researched as a solar photovoltaic material.^[9]