This Hemimorphite and Willemite specimen from M’Foutari, Republic of Congo formed within zinc-rich supergene zones created by the oxidation of primary sulfide ores. The soft blue, botryoidal hemimorphite developed under low-temperature, silica-rich conditions, forming layered, bubbly crusts with a velvety luster. Intergrown beneath and within these crusts is a darker, zinc-rich matrix consistent with willemite and associated oxidized material, clearly recording multiple stages of mineralization within the Congo Craton.

A defining feature of this specimen is its strong yellow fluorescence under ultraviolet light, caused primarily by willemite, one of the most fluorescent zinc minerals known. Willemite fluoresces intensely yellow to yellow-green due to manganese activator ions (Mn²⁺) within its crystal lattice, which emit visible light when excited by UV radiation. In this piece, the fluorescence dramatically highlights the internal structure and boundaries between mineral phases, often revealing zones that are subtle or nearly invisible under normal lighting.

Historically, M’Foutari material entered the collector market only in limited quantities during mid-to-late 20th century exploration, as mining in the region focused on base metals rather than specimen recovery. As a result, hemimorphite–willemite combinations from this locality are relatively uncommon. The combination of aesthetic blue hemimorphite, zinc-rich associations, and vivid UV response makes this specimen especially desirable to collectors who value not only visual appeal but also mineralogical and optical significance.

**Specimen from historic collection of Luiz Menezes, one of Brazil’s most respected mineral collectors from Brazil**

Approximate measurements: 57.87 x 42.83 x 22.39 mm

Weight: 57.85 g