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Sphalerite

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Sphalerite mineral is in group of Sulfide mineral that is formula ((Zn, Fe)S).It is the principal ore of zinc. Pure sphalerite is colorless and rare. Normally, iron is present, causing the color to vary from pale greenish yellow to brown and black with increasing iron content. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, and fluorite. Miners have also been known to refer to sphalerite as zinc blende, black-jack and ruby jack. Its complex crystals combine tetrahedral or dodecahedral forms with other faces. Sphalerite gets its name from the Greek sphaleros, meaning “deceitful,” because its lustrous dark crystals can be mistaken for other minerals. It is often coarsely crystalline or massive, or forms banded, botryoidal, or stalactitic aggregates. Sphalerite is found associated with galena in lead-zinc deposits. It occurs in hydrothermal vein deposits, contact metamorphic zones, and replacement deposits formed at high temperature (1,065°F/575°C or above). It is also found in meteorites and lunar rocks.

Name: From the Greek for treacherous, the mineral sometimes being mistaken for galena, but yielding no lead.

Association: Galena, chalcopyrite, marcasite, pyrite, fluorite, barite, quartz, many other hydrothermal minerals.

Polymorphism & Series: Trimorphous with matraite and wurtzite

Mineral Group: Sphalerite group.

Cell Data: Space Group: F43m. a = 5.4060 Z = 4

X-ray Powder Pattern: Synthetic ZnS. 3.123 (100), 1.912 (51), 1.561 (30), 2.705 (10), 1.240 (9), 1.1034 (9), 1.351 (6)

Economic importance: Sphalerite is the most important zinc ore. Approximately 95% of all primary zinc is extracted from sphalerite ores. However, due to the variable trace element content, sphalerite is an important source of many other elements such as cadmium, gallium, germanium and indium.

Varieties

In some examples the gray-black crystals have red iridescence; These are called “ruby sphalerites.” The pale yellow and red varieties have very little iron and are translucent. Darker, more opaque varieties contain more iron. Some samples are also fluorescent in ultraviolet light.

Pale samples from Gemmy, Franklin, New Jersey (see Franklin Quarry) are highly fluorescent orange and / or blue in long wave ultraviolet light and are known as cleiophane, an almost pure ZnS variety.

Composition

The chemical formula (Zn, Fe) of sphalerite is S. It is a zinc sulphide containing a variable amount of iron instead of zinc in the mineral lattice. The iron content is normally less than 25% by weight. The amount of iron substitution formed depends on the availability and temperature of the iron, with higher temperatures preferring a higher iron content.

Sphalerite generally contains small amounts of cadmium, indium, germanium or gallium trace. These rare elements are valuable and can be recovered as profitable by-products when they are abundant enough. Small amounts of manganese and arsenic may also be present in the sphalerite.

Chemical Properties

Chemical Classification Sulfide mineral
Formula (Zn,Fe)S
Common Impurities Mn,Cd,Hg,In,Tl,Ga,Ge,Sb,Sn,Pb,Ag

Sphalerite Physical Properties

Color Yellow, light to dark brown, black, red-brown, colourless, light blue. green
Streak Pale yellow to brown.
Luster Adamantine, Resinous
Cleavage Perfect Perfect {011}
Diaphaneity Transparent, Translucent
Mohs Hardness 3,5 – 4
Crystal System Isometric
Tenacity Brittle
Density 3.9 – 4.1 g/cm3 (Measured)    4.096 g/cm3 (Calculated)
Fracture Conchoidal
Crystal habit Euhedral crystals – occurs as well-formed crystals showing good external form. Granular – generally occurs as anhedral to subhedral crystals in matrix.
Other characteristics non-radioactive, non-magnetic, fluorescent and triboluminescent.

Sphalerite Optical Properties

Type Isotropic
RI values: nα = 2.369
Twinning Simple contact twins or complex lamellar forms, twin axis [111]
Birefringence Isotropic minerals have no birefringence
Relief Moderate

Sphalerite Occurrence

Formed under a wide range of low- to high-temperature hydrothermal conditions; in coal, limestone, and other sedimentary deposits.

Sphalerite, the most important ore of the zinc ore, is a very common mineral and is associated with galena, pyrite, marcasite, chalcopyrite, smithsonite, calcite and dolomite. In its formation and origin mode, it is closely related to the most common galena. It is widely distributed, but is mainly found in veins and irregular displacement beds in limestone. Sphalerite is also found in veins and contact metamorphic deposits in igneous rocks.

Uses Area

It is used as gemstone. Crystals of suitable size and transparency have been fashioned into gemstones, usually featuring the brilliant cut to best display sphalerite’s high dispersion of 0.156 (B-G interval), over three times that of diamond. Freshly cut gems have an adamantine luster. Owing to their softness and fragility the gems are often left unset as collectors or museum pieces (although some have been set into pendants).

The most important ore of zinc. The chief uses for metallic zinc, or spelter, are in galvanizing iron; making brass, an alloy of copper and zinc; in electric batteries; and as sheet zinc. Zinc oxide, or zinc white, is used extensively for making paint. Zinc chloride is used as a preservative for wood. Zinc sulfate is used in dyeing and in medicine. Sphalerite also serves as the most important source of cadmium.

Sphalerite Distribution

The most important ore of zinc. Only a few localities for the finest crystallized examples can be given.

  • In Germany, from Freiberg, Saxony, and Neudorf, Harz Mountains.
  • Colorless crystals in the Lengenbach quarry, Binntal, Valais, Switzerland.
  • At Hornı Slavkov (Schlaggenwald) and Prıbram, Czech Republic.
  • From Rodna, Romania. Transparent crystals in the Aliva mine, Picos de Europa Mountains, Cantabria [Santander] Province, Spain.
  • In England, from Alston Moor, Cumbria. At Dal’negorsk, Primorskiy Kray, Russia.
  • From Watson Lake, Yukon Territory, Canada.
  • In the USA, in the Tri-State district of the Mississippi Valley; near Baxter Springs, Cherokee Co., Kansas; Joplin, Jasper Co., Missouri and Picher, Ottawa Co., Oklahoma.
  • From the Elmwood mine, near Carthage, Smith Co., Tennessee; in the Eagle mine, Gilman district, Eagle Co., Colorado.
  • In Mexico, from Santa Eulalia and Naica, Chihuahua, and Cananea, Sonora.
  • At Huaron, Casapalca, and Huancavelica, Peru

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Wikipedia contributors. (2019, April 26). Sphalerite. In Wikipedia, The Free Encyclopedia. Retrieved 02:50, June 24, 2019, from https://en.wikipedia.org/w/index.php?title=Sphalerite&oldid=894261404
Cite this article as: Geology Science. (2019). Sphalerite. [online] Available at: http://geologyscience.com/minerals/sphalerite/ [5th December 2019 ]
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