Smithsonite

Smithsonite is a zinc carbonate mineral (ZnCO₃), historically mined as a zinc ore and named for the chemist James Smithson. Smithsonite forms as a secondary mineral in the oxidation zone of zinc ore deposits. When zinc sulfide minerals like sphalerite are exposed to weathering, the released zinc combines with carbonate-rich groundwater to precipitate smithsonite.

It typically forms in rounded, grape-like (botryoidal) masses rather than distinct crystals. The stunning color variety comes from trace elements: copper produces blue-green, cobalt creates pink to lavender, cadmium yields bright yellow, and manganese can add warm tones. Pure smithsonite is white to colorless.

The mineral was named after James Smithson, the British mineralogist whose bequest founded the Smithsonian Institution. He was the first to distinguish smithsonite from hemimorphite, minerals that had long been confused under the name 'calamine.'

Smithsonite's botryoidal habit, high specific gravity for a carbonate (noticeably heavy for its size), and pastel colors are diagnostic. It effervesces weakly in cold hydrochloric acid and vigorously when warmed.

Distinguish from hemimorphite (lighter, often forms blade-like crystals), prehnite (lower specific gravity, different habit), and chrysoprase (much harder, quartz family). The combination of bubbly surface texture, heaviness, and acid reaction narrows it down quickly.