Alpha-zinc sulfide

Alpha-zinc sulfide (α-ZnS) is the low-temperature polymorph of zinc sulfide, also known as sphalerite in its natural mineral form. It is one of two main crystalline modifications of ZnS, the other being beta-zinc sulfide (β-ZnS, wurtzite structure).

🌍 Origins and Naming

• Mineral Equivalent: Sphalerite (α-ZnS).
• Polymorphism:
  • α-ZnS (sphalerite structure): Stable at lower temperatures.
  • β-ZnS (wurtzite structure): Stable at higher temperatures.
• Synthetic Form: Produced industrially for pigments, phosphors, and semiconductors.

🔬 Chemical and Structural Properties

• Formula: ZnS
• Crystal System: Cubic (isometric, sphalerite type).
• Structure: Each Zn²⁺ is tetrahedrally coordinated by S²⁻ ions.
• Color: Pure ZnS is white; impurities can cause brown, yellow, or gray tones.
• Hardness: ~3.5–4 on Mohs scale.
• Density: ~4.0 g/cm³.
• Luster: Resinous to adamantine.
• Transparency: Transparent to translucent in pure form.

⚙️ Geological Occurrence

• Natural Form: Sphalerite is the chief ore of zinc, found in hydrothermal veins, sedimentary exhalative deposits, and skarns.
• Associated Minerals: Galena (PbS), chalcopyrite (CuFeS₂), pyrite (FeS₂).
• Localities: Worldwide — notable deposits in the USA (Missouri, Tennessee), Spain, and Australia.

📖 Scientific and Industrial Significance

• Ore Mineral: Sphalerite is the most important zinc ore.
• Semiconductors: Synthetic ZnS is used in optoelectronics, phosphors, and infrared optics.
• Pigments: Historically used as “lithopone” (ZnS + BaSO₄) for paints.
• Luminescence: Doped ZnS (with Cu, Ag, Mn) is used in phosphorescent and electroluminescent materials.

✨ Conclusion

Alpha-zinc sulfide (α-ZnS) is the cubic sphalerite polymorph of ZnS, stable at low temperatures and the dominant natural form. It is both the principal zinc ore and a technologically important material in optics and electronics.

In short: α-ZnS = sphalerite structure, cubic, main zinc ore, also used in semiconductors and pigments.