Willemite

Fine willemite on matrix from the world-famous Tsumeb Mine, Otavi Highlands, Namibia. The specimen shows blue to blue-green willemite forming well-developed crystalline aggregates on matrix, displaying a vitreous to slightly greasy luster. The colour and crystal development are characteristic of classic Tsumeb willemite material.

Willemite is a silicate mineral, first described in 1830 and named in honour of King William I of the Netherlands. It forms primarily in skarn and hydrothermal environments, and at Tsumeb occurs as a secondary mineral in the oxidation zone of the complex polymetallic orebody.

The Tsumeb Mine is one of the most important localities worldwide for willemite and is especially renowned for producing fine blue and green varieties. Willemite is considered uncommon to rare in well-crystallized cabinet-sized specimens, and examples of this size and quality are highly sought after by collectors. At Tsumeb, willemite is commonly associated with copper and lead minerals, and may occur together with quartz and secondary arsenates, which is typical for the locality.