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Sphalerite

Structure : Cubic
Hardness : 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