Sphalerite

Sphalerite is the primary zinc ore mineral, with the chemical formula ZnS. Also known as blende, it represents the most important source of this metal worldwide. The name derives from the Greek «sphaleros», meaning deceptive, due to the ease with which it was confused with other minerals by early miners.

Characteristics

Sphalerite exhibits a cubic crystal system with crystals that often adopt tetrahedral forms. Colors range from honey yellow to dark brown, to black when iron-rich. It possesses a very characteristic adamantine or resinous luster and a hardness of 3.5–4 on the Mohs scale. Cleavage is perfect parallel to the faces of the dodecahedron.

Genesis

It forms primarily in medium- to low-temperature hydrothermal deposits, often associated with galena, pyrite, and calcite. It is also common in sedimentary replacement deposits and metalliferous veins. Typical environments include contact metamorphic zones and lead–zinc deposits.

Varieties and curiosities

The main varieties are marmatite (iron-rich) and cleiophane (iron-poor). Industrially it is fundamental for the extraction of zinc, used in alloys, galvanization, and brass production. Historically it was considered a waste mineral in lead mines.

Importance for collectors

It is highly appreciated for its well-formed crystals and brilliant luster. Specimens with transparent yellow-orange crystals are particularly sought after. Value depends on crystal quality, transparency, and specimen size.

Italian localities

In Italy it is found mainly in Sardinia, in the mines of Iglesias and Monteponi. Notable specimens also come from the Alps, particularly from Valle d'Aosta, and from the mines of Trentino-Alto Adige, where it occurs as well-formed crystals.