Wulfenite with Calcite

Wulfenite with Calcite from the Xichang Mine, Liangshan Prefecture, Sichuan Province, China, measuring 75 × 42 × 33 mm and weighing 97 grams. A bright specimen of a species more usually associated with classic American localities, here from one of China's emerging sources.

Wulfenite is lead molybdate, PbMoO4, tetragonal, and it typically forms as thin tabular crystals ranging from pale yellow through orange to a deep, almost red-orange, the colour depending on trace impurities and the exact growth conditions. It forms in the oxidised zone of lead deposits where molybdenum, usually released from associated Molybdenite mineralisation, becomes available to combine with lead liberated from weathering Galena. Chinese localities in Sichuan and neighbouring provinces have become significant modern sources of well-formed Wulfenite over the past two decades, taking a place alongside the long-established Red Cloud Mine material from Arizona.

Having Calcite alongside the Wulfenite gives a sense of the wider mineral assemblage the oxidised zone produced, rather than an isolated single-species crystal. This piece is from the David Vince Collection.