Sphalerite Identification Guide

What Sphalerite Looks Like

Sphalerite (zinc sulfide, ZnS) is the chief ore of zinc and a striking mineral in its own right. Color ranges widely with iron content: pale yellow and green ('cleiophane', low iron) through honey-brown, orange-red ('ruby blende'), to nearly black ('marmatite', iron-rich). Its hallmark is a distinctive resinous to adamantine luster and, in gem-clear material, extraordinary fire (dispersion higher than diamond).

• Color: yellow, brown, red, green, black
• Transparency: transparent (low-iron) to opaque (iron-rich)
• Habit: isometric — tetrahedra and dodecahedra, often distorted; also massive, granular, and botryoidal

Step-by-Step Field-ID Checklist

1. Note the luster. A resinous, almost candy-like or 'sap' luster is a strong sphalerite tell.
2. Break or cleave a small fragment. Sphalerite has perfect cleavage in six directions (dodecahedral) — fragments break into many-faced shiny pieces.
3. Streak test. Rub on unglazed porcelain: streak is pale yellow to yellowish-brown to nearly white, which is much lighter than the often-dark crystal — a key surprise.
4. Look for triangular tetrahedral faces on crystals.
5. Check associations — galena, pyrite, fluorite, and dolomite are typical companions.

Key Diagnostic Tests

• Mohs hardness: 3.5–4 — softer than glass; a steel knife scratches it.
• Streak: pale yellow to light brown (diagnostic; lighter than expected).
• Cleavage: perfect dodecahedral, six directions — very diagnostic.
• Density: ~3.9–4.1 g/cm³, moderately heavy.
• Luster: resinous to adamantine.
• Odor: iron-rich sphalerite may give a faint rotten-egg (H₂S) smell with a drop of hydrochloric acid; it does not effervesce like a carbonate.
• Not magnetic.

Common Look-Alikes and How to Tell Them Apart

• Galena: lead-gray metallic with cubic cleavage and much higher density (~7.5); galena's streak is gray-black, sphalerite's is pale.
• Cassiterite: brown and adamantine but much harder (6–7) and far denser (~7); no good cleavage.
• Garnet: garnets are harder (6.5–7.5) and have no cleavage; sphalerite is soft with perfect six-way cleavage.
• Siderite / dolomite: carbonates effervesce in acid and have rhombohedral cleavage; sphalerite gives an H₂S odor but no fizzing.
• Wurtzite: same ZnS chemistry but hexagonal; usually requires lab confirmation.
• Amber / resin: truly resinous look, but amber is very light (~1.05, floats in saltwater) and soft, with no cleavage.

Where It Is Found

Sphalerite forms in hydrothermal veins and carbonate-hosted (Mississippi Valley-type) deposits. Famous sources include the Tri-State district (Missouri-Kansas-Oklahoma), Picos de Europa, Spain (fine gem crystals), Bulgaria, and Peru. It commonly occurs with galena, pyrite, chalcopyrite, fluorite, and dolomite.