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SPHALERITE:PHYSICAL CHARACTERISTICS:Color is typically black but can be brown, yellow, reddish, green, and less commonly white or colorless. Luster is adamantine or resinous or submetallic to earthy in massive forms. Transparency crystals are transparent to translucent. Crystal System is isometric; bar 4 3m Crystal Habits can be complicated with the rhombic dodecahedron, tetrahedron and combinations of these having cubic and tristetrahedron faces giving the crystals multiple faces of often indistinct forms. To add more confusion to the indistinct crystals, twinning is common and sometimes pervasive. Massive forms are common and can be granular, earthy, botryoidal, concretionary and fibrous. An aggregate of botryoidal crusts with layers of wurtzite and galena is called "Schalenblende" is sometimes cut and polished as an ornamental stone. Cleavage is perfect in six directions forming dodecahedrons. Fracture is conchoidal, but rarely seen because of frequent cleavage. Hardness is 3.5-4 Specific Gravity is approximately 4.0 (heavier than average, but light when compared to most metallic minerals) Streak is yellow to light brown (unusually light colored for a normally dark mineral). Other Characteristics: Striations on tetrahedral faces, triboluminescent (meaning it may glow if crushed), an index of refraction of 2.37 - 2.42, a dispersion (fire) of 0.156 and finally sphalerite is pyroelectric (meaning that it forms a slight electrical charge when heated or cooled). Associated Minerals almost always include galena, pyrite, fluorite, chalcopyrite, quartz, calcite, magnetite, pyrrhotite and many others. Notable Occurrences include Tri state area near Joplin, Missouri; Rosiclare, Illinois; Elmwood, Tennessee, USA; Broken Hill, Australia; Italy; Spain; Burma; Peru; Morocco; Germany and England. Best Field Indicators are crystal habits, streak, cleavage, high luster, softness and twinning. Sphalerite (which is also known as Blende), is an important ore of zinc and can make a rather attractive cabinet specimen as well. It can have excellent luster and associates with many beautifully colored minerals making it one of the best enhancers of many fine mineral specimens. Sphalerite is one of the very few minerals that has a total of six directions of cleavage. If all of them were to be perfectly cleaved on a single crystal it would form a rhombic dodecahedron. Identifying all six directions in a single cleaved crystal is quite difficult due to the multiple twinning and the many directions. Only the fact that there is abundant cleavage at different directions can easily be seen in most cleaved specimens. Sphalerite can be difficult to identify because of its variable luster, color, abundant but obscured cleavage and crystal habits. So difficult was sphalerite for miners to distinguish from more valuable minerals such as galena, acanthite and tetrahedrite, that they named it sphalerite which is Greek for treacherous rock and blende is German for blind or deceiving. The luster of sphalerite is truly its best attribute. It typically has a nice adamantine luster that really sparkles owing to its unusually high index of refraction and a fire greater than diamond's. Specimens of sphalerite are usually adorned with hundreds of small sparkling faces. Groups of faces can be symmetrically oriented into several different directions so that as a particularly gifted specimen is turned with respect to a viewer they are treated to several episodes of multiple and bright flashes. Transparent sphalerite has been cut for gemstones but its cleavage and softness limit its use as a gemstone to collectors only.
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