Euhedral crystals – occurs as well-formed crystals showing good external form. Granular – generally occurs as anhedral to subhedral crystals in matrix.
German geologistErnst Friedrich Glocker discovered sphalerite in 1847, naming it based on the Greek wordsphaleros, meaning "deceiving", due to the difficulty of identifying the mineral.[7]
In addition to zinc, sphalerite is an ore ofcadmium,gallium,germanium, andindium. Miners have been known to refer to sphalerite aszinc blende,black-jack, andruby blende.[8]Marmatite is an opaque black variety with a high iron content.[9]
Sphalerite crystallizes in theface-centered cubiczincblende crystal structure,[10] which was named after the mineral. This structure is a member of the hextetrahedral crystal class (space groupF43m). In the crystal structure, both the sulfur and the zinc or iron ions occupy the points of a face-centered cubic lattice, with the two lattices displaced from each other such that the zinc and iron are tetrahedrally coordinated to the sulfur ions, andvice versa.[11] Minerals similar to sphalerite include those in the sphalerite group, consisting of sphalerite,colaradoite,hawleyite,metacinnabar,stilleite andtiemannite.[12] The structure is closely related to the structure ofdiamond.[10] Thehexagonal polymorph of sphalerite iswurtzite, and the trigonal polymorph is matraite.[12] Wurtzite is the higher temperature polymorph, stable at temperatures above 1,020 °C (1,870 °F).[13] The lattice constant for zinc sulfide in the zinc blende crystal structure is 0.541nm.[14] Sphalerite has been found as apseudomorph, taking the crystal structure ofgalena,tetrahedrite,barite andcalcite.[13][15] Sphalerite can have Spinel Law twins, where the twin axis is [111].
The chemical formula of sphalerite is(Zn,Fe)S; the iron content generally increases with increasing formation temperature and can reach up to 40%.[6] The material can be considered a ternary compound between the binary endpointsZnS andFeS with composition ZnxFe(1-x)S, where x can range from 1 (pure ZnS) to 0.6.[citation needed]
All natural sphalerite contains concentrations of various impurities, which generally substitute for zinc in the cation position in the lattice; the most common cation impurities arecadmium,mercury andmanganese, butgallium,germanium andindium may also be present in relatively high concentrations (hundreds to thousands of ppm).[16][17] Cadmium can replace up to 1% of zinc and manganese is generally found in sphalerite with high iron abundances.[12] Sulfur in the anion position can be substituted for byselenium andtellurium.[12] The abundances of these impurities are controlled by the conditions under which the sphalerite formed; formation temperature, pressure, element availability and fluid composition are important controls.[17]
Sphalerite possesses perfect dodecahedralcleavage, having six cleavage planes.[10][18] In pure form, it is a semiconductor, but transitions to a conductor as the iron content increases.[19] It has a hardness of 3.5 to 4 on theMohs scale of mineral hardness.[20]
It can be distinguished from similar minerals by its perfect cleavage, its distinctive resinous luster, and the reddish-brown streak of the darker varieties.[21]
Sphalerite fluorescing under ultraviolet light (Sternberg Museum of Natural History, Kansas, US)
Purezinc sulfide is awide-bandgap semiconductor, with bandgap of about 3.54 electron volts, which makes the pure material transparent in the visible spectrum. Increasing iron content will make the material opaque, while various impurities can give the crystal a variety of colors.[20] In thin section, sphalerite exhibits very high positiverelief and appears colorless to pale yellow or brown, with nopleochroism.[6]
Therefractive index of sphalerite (as measured via sodium light, average wavelength 589.3 nm) ranges from 2.37 when it is pure ZnS to 2.50 when there is 40% iron content.[6] Sphalerite is isotropic under cross-polarized light, however sphalerite can experiencebirefringence if intergrown with its polymorph wurtzite; the birefringence can increase from 0 (0% wurtzite) up to 0.022 (100% wurtzite).[6][13]
Depending on the impurities, sphalerite willfluoresce under ultraviolet light. Sphalerite can betriboluminescent.[22] Sphalerite has a characteristic triboluminescence of yellow-orange. Typically, specimens cut into end-slabs are ideal for displaying this property.[citation needed]
Gemmy, colorless to pale green sphalerite fromFranklin, New Jersey (seeFranklin Furnace), are highly fluorescent orange and/or blue under longwave ultraviolet light and are known ascleiophane, an almost pure ZnS variety.[23] Cleiophane contains less than 0.1% of iron in the sphalerite crystal structure.[12] Marmatite or christophite is an opaque black variety of sphalerite and its coloring is due to high quantities of iron, which can reach up to 25%; marmatite is named afterMarmato mining district inColombia and christophite is named for the St. Christoph mine inBreitenbrunn,Saxony.[23] Both marmatite and cleiophane are not recognized by theInternational Mineralogical Association (IMA).[24] Red, orange or brownish-red sphalerite is termed ruby blende or ruby zinc, whereas dark colored sphalerite is termed black-jack.[23]
Similar to SEDEX, Mississippi-Valley type (MVT) deposits are also a Pb-Zn deposit which contains sphalerite.[35] However, they only account for 15–20% of zinc and lead, are 25% smaller in tonnage than SEDEX deposits and have lower grades of 5–10% Pb + Zn.[33] MVT deposits form from the replacement of carbonate host rocks such as dolostone and limestone by ore minerals; they are located in platforms and foreland thrust belts.[33] Furthermore, they are stratabound, typically Phanerozoic in age and epigenetic (form after the lithification of the carbonate host rocks).[36] The ore minerals are the same as SEDEX deposits: sphalerite, galena, pyrite, pyrrhotite and marcasite, with minor sulfosalts.[36] Mines that contain MVT deposits include Polaris in the Canadian arctic, Mississippi River in theUnited States, Pine Point in Northwest Territories, and Admiral Bay in Australia.[37]
Volcanogenic massive sulfide (VMS) deposits can be Cu-Zn- or Zn-Pb-Cu-rich, and accounts for 25% of Zn in reserves.[33] There are various types of VMS deposits with a range of regional contexts and host rock compositions; a common characteristic is that they are all hosted by submarine volcanic rocks.[32] They form from metals such as copper and zinc being transferred by hydrothermal fluids (modified seawater) which leach them from volcanic rocks in the oceanic crust; the metal-saturated fluid rises through fractures and faults to the surface, where it cools and deposits the metals as a VMS deposit.[38] The most abundant ore minerals are pyrite, chalcopyrite, sphalerite and pyrrhotite.[33] Mines that contain VMS deposits includeKidd Creek in Ontario, Urals inRussia, Troodos inCyprus, and Besshi inJapan.[39]
Sphalerite is an important ore of zinc; around 95% of all primary zinc is extracted from sphalerite ore.[42] However, due to its variable trace element content, sphalerite is also an important source of several other metals such as cadmium,[43] gallium,[44] germanium,[45] and indium[46] which replace zinc. The ore was originally calledblende by miners (from Germanblind ordeceiving) because it resembles galena but yields no lead.[21]
The zinc in sphalerite is used to producebrass, an alloy of copper with 3–45% zinc.[18] Major element alloy compositions of brass objects provide evidence that sphalerite was being used to produce brass by the Islamic as far back as themedieval ages between the 7th and 16th century CE.[47] Sphalerite may have also been used during the cementation process of brass in Northern China during the 12th–13th century CE (Jin Dynasty).[48] Besides brass, the zinc in sphalerite can also be used to produce certain types of bronze; bronze is dominantly copper which is alloyed with other metals such as tin, zinc, lead, nickel, iron and arsenic.[49]
Faceted sphalerite, known by the name of Étoile des Asturies, one of the largest in existence. It actually comes from the Aliva mine, Cantabria (Spain). Cantonal Museum of Geology of Lausanne.
Galvanized iron – zinc from sphalerite is used as a protective coating to prevent corrosion and rusting; it is used on power transmission towers, nails and automobiles.[41]
^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005)."Sphalerite"(PDF).Handbook of Mineralogy. Mineral Data Publishing. Retrieved14 March 2022.
^Klein, Cornelis; Hurlbut, Cornelius S. Jr. (1993).Manual of mineralogy : (after James D. Dana) (21st ed.). New York: Wiley. pp. 211–212.ISBN047157452X.
^abFrenzel, Max; Hirsch, Tamino; Gutzmer, Jens (July 2016). "Gallium, germanium, indium, and other trace and minor elements in sphalerite as a function of deposit type — A meta-analysis".Ore Geology Reviews.76:52–78.Bibcode:2016OGRv...76...52F.doi:10.1016/j.oregeorev.2015.12.017.
^Craddock, P.T. (1990).Brass in the medieval Islamic world; 2000 years of zinc and brass. British Museum Publications Ltd. pp. 73–101.ISBN0-86159-050-3.
Webster, R., Read, P. G. (Ed.) (2000).Gems: Their sources, descriptions and identification (5th ed.), p. 386. Butterworth-Heinemann, Great Britain.ISBN0-7506-1674-1
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