Sphalerite
Structure : CubicHardness : 3.5
Specific Gravity : 4.09
Refractive index : 2.36 - 2.3
Doubly Refracting (bi-refraction) : none
Sphalerite has extremely high dispersion, more so than diamond. One of the few known gems that compares to the luster of diamond. Rarely found facet grade with Santander Spain, the area known for most of the worlds finest Sphalerite gems. Unfortunately, little to no mining occurs any more, as the mines have flooded and caved in.
Sphalerite Properties Absorption Spectrum: Sometimes 3 bands seen in the red at 6900, 6670, and 6510 due to cadmium.
Birefringence: None
Cleavage: Perfect dodecahedral
Colors: Colorless (very rarely); black (rich in Fe), brown, orange, yellow, green, red, orange-red, white-gray. May show color zoning.
Crystallography: Isometric. Crystals widespread, in various shapes; massive, cleavable, granular.
Dispersion: 0.156 (extremely high)
Etymology: From the Greek sphaleros, meaning 'treacherous,' because sphalerite often resembles galena (lead sulfide) but yields no lead.
Formula: ZnS + Fe
Fracture: Conchoidal
Hardness: 3.5-4
Heat Sensitivity: Yes
Luminescence: Bright orange-red to red in LW, SW, from many localities. Material from Otavi, Namibia is triboluminescent. (Produces light under friction).
Luminescence Present: Yes
Luminescence Type: Fluorescent, UV-Long, UV-Short
Luster: Resinous to adamantine
Occurrence: Sphalerite is the chief ore of zinc, the most abundant zinc mineral, and is common in low-temperature ore deposits, especially in limestones; also in sedimentary rocks; hydrothermal ore veins.
Optics: Isotropic; N = 2.37-2.50. (Spanish material 2.40).
Pleochroism: None
Refractive Index: 2.37-2.50
Specific Gravity: 3.90-4.10
Transparency: Transparent to opaque
Variety of Lesser Known Gemstones
Wearability: Poor