Sphalerite
Sphalerite (Zinc sulfide) · Mineral Specimen and Collector Gemstone
Crystal System
Isometric (Cubic); typically occurs in tetrahedral or dodecahedral crystals, but commonly found in massive, granular, or botryoidal habits.
Mineral Group
Sulfides
Chemical Formula
(Zn,Fe)S
Formation Process
Primarily hydrothermal, forming from hot, mineral-rich fluids in low to moderate temperature environments. Often associated with galena, fluorite, and barite.
About This Crystal
This specimen exhibits a dark, brownish-black color with a high sub-metallic to resinous luster. It appears opaque to translucent on thin edges. The surface is irregular and wet in the image, accentuating its reflective properties and granular texture.
Physical Characteristics
Color: Yellow, brown, black (due to iron content), or red; Streak: White to pale yellow-brown; Cleavage: Perfect in six directions (dodecahedral); Fracture: Uneven to conchoidal; Specific Gravity: 3.9–4.2; Fluorescence: Often orange to red under longwave UV.
Optical Properties
Refractive Index: 2.37 (extremely high); Birefringence: None (singly refractive); Dispersion: 0.156 (over three times that of diamond, though often masked by deep body color).
Hardness & Durability
Origin Region
Notable sources include the Tri-State district (USA), Aliva (Spain), Maramures (Romania), and various localities in Peru and China. It forms in hydrothermal veins and carbonate-hosted deposits.
Hardness & Durability
Mohs Hardness: 3.5 to 4.0. It is relatively soft and brittle with perfect cleavage, making it susceptible to scratching and breakage. Most suitable for collector specimens rather than everyday jewelry.
Care & Maintenance
Clean only with warm, soapy water and a soft cloth; avoid ultrasonic or steam cleaners. Store separately from harder minerals to prevent scratching. Sensitive to strong acids.
Rarity & Value
Common as an industrial ore of zinc, but high-quality crystalline or gem-grade material is uncommon. Value is based on crystal perfection, transparency (for faceted gems), and color.
Special Characteristics
High dispersion leads to intense fire in transparent specimens. It is the primary ore of zinc and can contain significant traces of cadmium, indium, and gallium.
Lore & History
Historically known as 'Zinc Blende' or 'Black Jack' by miners. Its name is derived from the Greek 'sphaleros' meaning treacherous or deceptive, because it looked like galena but yielded no lead. Traditionally associated with grounding and energy balance in mineral lore.