Mimetite is a mineral composed of lead arsenate chloride (Pb5(AsO4)3Cl) that typically forms as a secondary mineral in lead deposits through the oxidation of galena and arsenopyrite. Its name is derived from the Greek word Μιμητής mimetes, which translates to "imitator," highlighting its similarity to the mineral pyromorphite. This similarity is significant, as mimetite is part of a mineral series that includes both pyromorphite (Pb5(PO4)3Cl) and vanadinite (Pb5(VO4)3Cl). Noteworthy locations for mimetite include Mapimi in Durango, Mexico, and Tsumeb in Namibia.
Willemite is a zinc silicate mineral (Zn2SiO4) and serves as a minor source of zinc. It exhibits strong green fluorescence when exposed to shortwave ultraviolet light and presents a range of colors in natural light, often found in fibrous and vibrant apple-green forms. Troostite, a variant of willemite, features partial replacement of zinc with manganese and is typically found in solid brown formations.
This mineral was first identified in 1829 at the Vieille-Montagne mine in Belgium, where Armand Lévy received samples from a university student. He named the mineral in honor of William I of the Netherlands, although it is sometimes referred to as villemite. The troostite variant is named after the Dutch-American mineralogist Gerard Troost.
