sphalerite

[Greek sphaleros, slippery, deceitful (from sphallein, to trip, from its being easily mistaken for galena) + -ITE¹.]

(click to enlarge)
Sphalerite from Baxter Springs, Kan. (credit: Courtesy of the Ted and Elsie Boente Collection; photograph, John H. Gerard — EB Inc.)

Zinc sulfide (ZnS), the chief ore mineral of zinc. It is found associated with galena in most important lead-zinc deposits. The most important deposits are in the Mississippi River valley (U.S.), Poland, Belgium, and North Africa. See also sulfide mineral.

For more information on sphalerite, visit Britannica.com.

A mineral, β-ZnS, also called blende. It is the low-temperature form and more common polymorph of ZnS, Pure β-ZnS on heating inverts to wurtzite, α-ZnS, at 1868°F (1020°C).

The mineral is most commonly in coarse to fine, granular, cleavable masses. The luster is resinous to submetallic; the color is white when pure, but is commonly yellow, brown, or black, darkening with increased percentage of iron. There is perfect dodecahedral cleavage; the hardness is 3½ on Mohs scale; specific gravity is 4.1 for pure sphalerite.

Sphalerite is a common and widely distributed mineral. It occurs both in veins and in replacement deposits in limestones. As the chief ore mineral of zinc, sphalerite is mined on every continent. The United States is the largest producer, followed by Canada, Mexico, Russia, Australia, Peru, the Congo River area, and Poland. See also Wurtzite; Zinc.

Environment

In sulfide ore veins in all rock classes, under the same conditions responsible for galena.

Tetrahedral crystals very common, sometimes so completely developed as to look octahedral. Cube, dodecahedron, and tristetrahedron faces also present, the latter often rounded so that it is difficult to distinguish the faces. Also stalactitic, granular, and massive.

Colorless (very rare) through yellow and green to red-brown and black. Luster adamantine to resinous; hardness 3Ɖ-4; specific gravity 3.9-4.1; streak white to cream; fracture conchoidal; cleavage perfect dodecahedral. Brittle; transparent (even gemmy) to opaque; interesting luminescent effects (see below); occasionally fluorescent.

Zinc sulfide (67.0% Zn, 33.0% S with varying amounts of cadmium, iron, manganese, and other elements).

Practically infusible on charcoal, but develops a coating on and around a chip that is yellow when hot and white when cold. Touched with cobalt solution, the yellow coating becomes green in the reducing flame (the addition of Na ₂ CO ₃ powder facilitates this test). Dissolves reluctantly in hydrochloric acid with bubbles of hydrogen sulfide (rotten-egg smell).

When it is very black its high luster and easy cleavage gives it a resemblance to galena, but the light streak, the powder, and any blowpipe test suffice for this distinction. Resembles some siderite, but can be distinguished by remaining nonmagnetic after roasting and by its higher gravity. The characteristic luster and association with pyrite and galena generally serve to identify sphalerite.

Same as galena, with which it is usually associated. Localities are almost too numerous to mention, but the gemmy, transparent light yellow to red Santander (Spain) masses are notable. Joplin District (Missouri, Kansas, and Oklahoma) crystals range from black and dull irregular giants to minute red ("ruby jack") incrustations. The palest U.S. specimens are light yellow-green crystals from Franklin, New Jersey, and colorless in Balmat, New York. Trepça, in the former Yugoslavia, has become an important source of good "black jack" specimens, as has the Nicolaj Mine, Dolnegorsk, Russia, and a mine in Madan, Bulgaria.

Sphalerite is the principal ore of zinc. It alters to hemimorphite, smithsonite, and willemite. Impurities recovered in smelting--gallium, indium, and cadmium--make it also the chief ore of those metals. Its cleavage and luminescent responses make it of particular interest to mineral collectors. It is the best mineral example of dodecahedral cleavage, and with care perfect dodecahedrons can be cleaved out. Sometimes it fluoresces orange in ultraviolet light. Fluorescent sphalerite also shows the infrequent phenomenon of triboluminescence; that is, it emits flashes of orange light on being firmly stroked with a hard substance such as a knife or a stone. Though too soft for use, rare-gem collectors treasure the fiery brilliants that may be cut from the light-hued Picos de Europa, Santander (Spain) specimens.

Sphalerite
General
Category	Sulfide mineral
Chemical formula	(Zn,Fe)S
Strunz classification	02.CB.05a
Dana classification	02.08.02.01
Identification
Color	Brown, yellow, red, green, black.
Crystal habit	Euhedral Crystals - Occurs as well-formed crystals showing good external form. Granular - Generally occurs as anhedral to subhedral crystals in matrix. Colloform
Crystal system	Isometric hextetrahedral (4 3m)
Twinning	Simple contact twins or complex lamellar forms, twin axis [111]
Cleavage	[110] Perfect
Fracture	Uneven to conchoidal
Mohs scale hardness	3.5-4
Luster	Adamantine, resinous, greasy
Streak	brownish white, pale yellow
Diaphaneity	Transparent to translucent, opaque when iron-rich
Specific gravity	3.9 - 4.2
Optical properties	Isotropic
Refractive index	nα = 2.369 ZnS
Other characteristics	non-radioactive, non-magnetic, Fluorescent and triboluminescent.
References	[1][2][3]

"Zincblende" redirects here. For the crystal structure, see Zincblende (crystal structure).

Sphalerite ((Zn,Fe)S) is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. 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, mock lead, false galena and black-jack.

The crystal structure of sphalerite

The mineral crystallizes in the cubic crystal system. In the crystal structure, zinc and sulfur atoms are tetrahedrally coordinated. The structure is closely related to the structure of diamond. The hexagonal analog is known as the wurtzite structure. The lattice constant for zinc sulfide in the zincblende crystal structure is 0.596 nm, calculated from geometry and ionic radii of 0.074 nm (zinc) and 0.184 nm (sulfide). It forms ABCABC layers.

Its color is usually yellow, brown, or gray to gray-black, and it may be shiny or dull. Its luster is adamantine, resinous to submetallic for high iron varieties. It has a yellow or light brown streak, a hardness of 3.5 - 4, and a specific gravity of 3.9-4.1. Some specimens have a red iridescence within the gray-black crystals; these are called "ruby sphalerite." The pale yellow and red varieties have very little iron and are translucent. The darker more opaque varieties contain more iron. Some specimens are also fluorescent in ultraviolet light. The refractive index of sphalerite (as measured via sodium light, 589.3 nm) is 2.37. Sphalerite crystallizes in the isometric crystal system and possesses perfect dodecahedral cleavage. Gemmy, pale specimens from Franklin, New Jersey (see Franklin Furnace) are highly fluorescent orange and/or blue under longwave ultraviolet light and are known as cleiophane, an almost pure ZnS variety.

Another sphalerite sample

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 are lively with an adamantine luster and could conceivably be mistaken for a fancy-colored diamond in passing, but due to sphalerite's softness and fragility the gems are best left unset as collector's or museum pieces (although some have been set into pendants). Collectors may pay a premium for stones over one carat (200 mg), as clean crystals are usually quite small. Gem-quality material is usually a yellowish to honey brown, red to orange, or green; the two most important sources are the Chivera mine, Cananea, Sonora, Mexico; and the Picos de Europa, Cordillera Cantabrica, near Santander on Spain's northern coast.

References

1. ^ http://webmineral.com/data/Sphalerite.shtml Webmineral
2. ^ http://www.mindat.org/min-3727.html Mindat.org
3. ^ http://rruff.geo.arizona.edu/doclib/hom/sphalerite.pdf Handbook of Mineralogy

• Dana's Manual of Mineralogy ISBN 0-471-03288-3
• Webster, R., Read, P. G. (Ed.) (2000). Gems: Their sources, descriptions and identification (5th ed.), p. 386. Butterworth-Heinemann, Great Britain. ISBN 0-7506-1674-1
• Minerals.net
• Minerals of Franklin, NJ

See also

• List of minerals

External links

Wikimedia Commons has media related to: Sphalerite

• The sphalerite structure
• Possible relation of Sphalerite to origins of life and precursor chemicals in 'Primordial Soup'

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