Sphalerite

While sphalerite holds limited cultural prominence, its high dispersion and brilliance have led to occasional use as a faceted collector's gem. Historically, its confusing similarity to galena influenced mining lore and terminology, with miners coining names like "black-jack" and "blende." Today, sphalerite is valued more for its industrial importance than for artistic or mythological associations.

• Sphalerite is the chief ore of zinc, accounting for the majority of global zinc production.
• Its name means "treacherous" in Greek, reflecting its deceptive resemblance to galena.
• The mineral exhibits perfect cleavage in six directions—unusual among common minerals.
• Transparent varieties, called cleiophane, are prized by collectors for their high dispersion and brilliance.
• Sphalerite can contain trace amounts of cadmium, making it a secondary source for this element.

Sphalerite's chemical formula is ZnS, representing zinc sulfide. The mineral consists of zinc and sulfur atoms in a 1:1 ratio, with occasional trace elements such as iron and cadmium substituting within the crystal lattice.

Sphalerite crystallizes in the isometric (cubic) crystal system. Its typical crystal forms are tetrahedral and dodecahedral, and the structure is characterized by a highly symmetrical arrangement of zinc and sulfur atoms. The mineral exhibits perfect dodecahedral cleavage, a hallmark of its internal symmetry.

• Hardness: 3.5–4.0 on the Mohs scale
• Color: Ranges from colorless, yellow, brown, red, green, to black (varies with iron content)
• Luster: Resinous to adamantine
• Streak: White to pale yellow
• Cleavage: Perfect in six directions (dodecahedral)
• Fracture: Uneven to conchoidal
• Density: 3.9–4.1 g/cm³
• Transparency: Transparent to translucent
• Optical properties: High refractive index (2.368–2.371)

Sphalerite is most commonly found in hydrothermal vein deposits, sedimentary exhalative deposits, and metamorphosed carbonate rocks. It frequently occurs alongside minerals such as galena, pyrite, chalcopyrite, and fluorite. Major localities include the Tri-State District in the USA, Broken Hill in Australia, and the Santander region in Spain, making sphalerite a globally distributed and economically significant mineral.

• Varieties: Cleiophane (transparent, gem-quality sphalerite)
• Synonyms: Blende, zinc blende, black-jack (miners' slang), cleiophane

Sphalerite is the primary ore of zinc, a metal essential for galvanization, alloy production, batteries, and numerous chemical applications. It also serves as a minor gemstone (cleiophane) and can be a source of cadmium when present as an impurity. The mineral's role in zinc extraction underpins industries from construction to electronics.

• Look for resinous to adamantine luster and variable color, often brown to black.
• Test for perfect cleavage in six directions—distinctive for sphalerite.
• Check streak color: sphalerite leaves a white to pale yellow streak.
• Note associations with galena and pyrite in ore deposits.
• Transparent varieties may show high brilliance and dispersion.

• Store sphalerite specimens away from acids, as the mineral is soluble in hydrochloric acid.
• Handle with care: sphalerite can be brittle, especially iron-rich varieties.
• Clean gently with a soft brush and water; avoid harsh chemicals.
• Protect from sharp impacts to prevent cleavage-related breakage.

Notable sphalerite specimens have been recovered from the Tri-State District (USA), Broken Hill (Australia), and Santander (Spain), often displaying large, lustrous crystals. Transparent cleiophane crystals from Spain and Mexico are especially prized by collectors for their gem-like appearance and high dispersion.