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Properties of Sphalerite

The mineral sphalerite has many physical properties like color, luster and crystalline structure. The chemical formula of its purest form is ZnS and its chemical compound name is zinc sulfide. This mineral is not always pure and is often found contaminated with other elements and compounds. Most commonly, the element iron replaces some of the zinc in this mineral's crystalline structure. Sphalerite derives it name from the Greek word "sphaleros," which means treacherous. Sphalerite was often mistaken for a mineral valued by the Greeks known as galena. Sphalerite is found worldwide, commonly near hydrothermal vents. Prime specimens of spharelite have been found in the Upper Mississippi Valley in the states of Missouri, Kansas and Tennessee.

Color
- The purest forms of sphalerite are shades of a deep transparent yellow to orange. Sometimes spharelite is red and this is called ruby blende or strawberry jack because its large red crystals are approximately the size and color of a strawberry. When sphalerite contains significant amounts of manganese, it turns black. If iron is present, the crystals have a black metallic sheen. Other rare colors of spharelite are grayish blue, dark green and deep purple.
Luster
- Sphalerite usually has an adamantine luster. Luster is the sheen or soft glow given off from the reflective surface of a mineral. Sphalerite's sheen is sparkly like that of diamond or other gemstone. Sphalerite is prized for its beauty but its value is tempered by its brittleness. Though its highly reflective and can be cut into glittering forms, it is not suitable for jewelry because it easily breaks. At times, sphalerite's luster can also appear to be fibrous similar to the material asbestos. It's also found in resinous forms that have a sheen, like chewed bubble gum or dried glue.
Crystalline Forms
- Common structures of sphalerite are large to drusy crystals where surfaces are encrusted with tiny crystals. Sphalerite's crystalline systems are isometric. Each edge of a sphalerite crystal is the same length. Crystals tend to be tetrahedral or dodecahedral but the shapes are often distorted. Sphalerite crystals with conical faces are common with lengths of up to 30 cm. Another crystal shape of sphalerite is stalactite, a tapering structure like an icicle. Sometimes this mineral is found in coarse to fine granular forms.
Other Properites
- When sphalerite is cleaved, it smells like matchsticks because of the presence of sulfur. It makes a white to yellow streak when it scratches a hard surface. Many specimens of this mineral are translucent or even transparent, though it is occasionally opaque. This mineral has fluorescent properties and might glow orange under an ultraviolet light. It can also glow when it is crushed. It also has a mild pyroelectric property. When heated or cooled, it forms a slight electrical charge.

Rocks & Minerals