Kesterite

Kesterite is a sulfide mineral with the chemical formula Cu2ZnGeS4. It is a member of the kesterite-stannite series of copper germanium sulfides, exhibiting a tetragonal crystal structure. In natural samples, zinc and germanium are ordered on distinct lattice sites, distinguishing kesterite from the iron-rich endmember stannite, Cu2FeGeS4.

Kesterite forms in hydrothermal ore deposits, commonly found as veins with sphalerite, galena, pyrite, and other copper sulfides. It is relatively rare and of mainly academic interest; specimens are sought by mineral collectors. The mineral displays a metallic to submetallic luster and ranges in color from yellowish bronze to brown; it is opaque and has a moderate to good hardness for a sulfide.

The composition and ordered structure of kesterite have attracted attention in materials science because Cu2ZnGeS4 can be used as a model compound for related photovoltaic absorbers, such as copper zinc germanium sulfide selenide. In practice, the natural mineral is not a primary ore source and is not used commercially for photovoltaics; instead, synthetic kesterite-based materials are studied for thin-film solar cells.