Sphalerite

sphalerite

galena

zinc

wurtzite

Images

Formula: ZnS
Sulphide, isometric polytype of trigonal or hexagonal wurtzite. Wurtzite is the high temperature polytype; the transition for pure ZnS occurs at 1020oC, and this transition temperature is lowered by the presence of iron in solid solution ( AM 46.1382).

Varieties

Cleiophane is a light-coloured to colourless variety of sphalerite with low Fe and Mn content

Specific gravity: 3.9 to 4.2
Hardness: 3½ to 4
Streak: White, yellow to brown if iron is present
Colour: Yellow, brown, red, green, black, rarely colourless
Solubility: Moderately soluble in hydrochloric acid; slightly soluble in nitric acid; insooluble in water
Common impurities: Mn,Cd,Hg,In,Tl,Ga,Ge,Sb,Sn,Pb,Ag
Environments:

Igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Sphalerite is extremely common. Its occurrence and mode of origin are similar to those of galena, with which it is commonly found. Sphalerite occurs in granite, gabbro, sedimentary deposits and contact metamorphic deposits. It is found as a primary mineral in hypothermal (high temperature) hydrothermal veins associated with arsenopyrite, galena and quartz, and in replacement deposits associated with chalcopyrite, galena and pyrite.
Sphalerite with only minor galena occurs associated with pyrrhotite, pyrite and magnetite.
It also may be found in gabbro and granite.
In the oxidised zone of epithermal veins, sphalerite (primary) alters to secondary hemimorphite, smithsonite and manganese-bearing willemite.

Localities

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. Sphalerite is a primary sulphide that occurs as aggregates in chloritic rocks at the Two Mile deposit. Associated minerals include chalcopyrite and galena (AJM 22.1.37-38).

At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the deposit has been mined for oxide and supergene copper ores, predominantly malachite, azurite and chrysocolla. The ores overlie primary zone mineralisation consisting of quartz-dolomite-sulphide veins hosted in dolomite-bearing siltstone and graphitic schist.
Sphalerite occurs rarely rimming pyrite and chalcopyrite and as inclusions in pyrite. Paragenesis for the primary zone is dolomite followed by pyrite, then chalcopyrite and sphalerite, and lastly bornite (AJM 22.1.20 & 25).

At the Mount Deverell variscite deposit, Milgun Station, Western Australia, rare grains of sphalerite have been found as inclusions in grains of quartz in siltstone enclosing variscite veins. The variscite deposits are hosted by marine sedimentary rocks (AJM 20.2.29).

At the Blue Points mine, Thunder Bay, Ontario, Canada, sphalerite is associated with calcite and minor chalcopyrite in silicified mudstone breccia (R&M 94.4.330).

At the Lin Ma Hang mine, North District, New Territories, Hong Kong, China, the lead-zinc deposit is a hydrothermal deposit which lies along a fault zone within altered acid volcanic rocks, consisting mainly of chlorite, biotite, sericite and actinolite, with scattered quartz. (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
The mineralisation consists of a series of fissure vein deposits varying from a few mm to several metres on width. The initial vein filling was coarse milky quartz. this was followed by an intrusion of fine-grained quartz carrying the metallic minerals, galena, pyrite, sphalerite and chalcopyrite, in order of abundance (Geological Society of Hong Kong Newsletter, 9.4.3-27).

At Devil's Peak, Sai Kung District, New Territories, Hong Kong, China, the mineralisation occurred in quartz veins in the contact zone between a granite intrusion and acid volcanic rocks. The mine is now closed, and inaccessible for collecting. Sphalerite occurred in some of the beryl-wolframite containing quartz veins (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Needle Hill Mine, Needle Hill, Sha Tin District, New Territories, Hong Kong, China, is a tungsten mine, abandoned in 1967. The principal ore is wolframite, and the principal gangue mineral is quartz. Molybdenum also occurs. The mineralisation consists of a series of parallel fissure veins that cut through granite. Wolframite and quartz are the main minerals, but galena, sphalerite, pyrite, molybdenite and fluorite have also been found here (Geological Society of Hong Kong Newsletter 9.3.29-40). The quartz-wolframite veins are of high-temperature hydrothermal formation, and grade into wolframite-bearing pegmatites.
Sphalerite is a common accessory mineral in the wolframite-bearing quartz veins and pegmatites (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

At Chuen Lung, Tsuen Wan District, New Territories, Hong Kong, China, in fissure veins in granite rocks in a small stream near Chuen Lung, silver-bearing galena occurs associated with massive granular amber coloured sphalerite, chalcopyrite, pyrite and pyrrhotite (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Lin Fa Shan deposit, Tsuen Wan District, New Territories, Hong Kong, China, is located in a remote area of the Tai Mo Shan Country Park, on a steep west facing slope of Lin Fa Shan, just above the abandoned village of Sheung Tong. The surrounding hillsides are covered with shallow excavations, representing past searches for wolframite, the natural ore of tungsten. The abandoned workings are extremely dangerous with unsupported tunnels, open shafts and no maintenance since their closures in 1957; the workings should not be entered (http://industrialhistoryhk.org/lin-shan).
Sphalerite is common in wolframite-bearing quartz veins (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).

At Berg Aukas, Grootfontein, Otjozondjupa Region, Namibia, sphalerite is partially oxidised from near-surface to depths of around 600 m. It contains trace amounts of iron, cadmium, manganese and germanium (R&M 96.2.136-140) The paragenetic sequence for the sulphides is proposed to be pyrite (oldest) - bornite - chalcopyrite - tennantite-sphalerite-galena-enargite-germanite-renierite-tetrahedrite - jordanite (youngest) (R&M 96.2.113)

At the Free State Geduld Mine, Welkom, Lejweleputswa District, Free State, South Africa, the largest sphalerite crystals from southern Africa, measuring up to 6.2 cm, have been collected from a fault zone. Associated minerals include pyrrhotite, pyrite, quartz and galena (R&M 96.4.343).

At the Randfontein Estates Mine, West Rand District, Gauteng, South Africa, a specimen of yellow baryte overgrown on tetrahedral, striated sphalerite has been found (R&M 96.4.343).

At the Mponeng Mine, West Wits, Far West Rand, West Rand District Municipality, Gauteng, South Africa, finely crystallised sphalerite has been found forming rims on the edges of pyrrhotite or partially coating galena, also some large individual stepped tetrahedral crystals of sphalerite to 3 cm have been found. Cleavage fragments yield a ruby-red translucency (R&M 96.4.343).

At Aggeneys, Namakwa, Northern Cape, South Africa, siderite pseudomorphs after sphalerite have been found (KL p160).

At Alderley Edge, Cheshire, England, UK, copper mineralised solutions percolated through porous sandstone and deposited barium, cobalt, copper, lead, vanadium and zinc minerals between the sand grains. Anhydrite formed as cement in permeable rocks, then baryte was deposited, followed by pyrite, chalcopyrite, sphalerite and galena (RES pps 49-50).

At the Boltsburn Mine, Rookhope, Weardale, County Durham, England, UK, sphalerite is associated with fluorite (SY p172)

At Force Crag Mine, Coledale, Above Derwent, Allerdale, Cumbria, England, UK, a specimen has been found with a quartz matrix covered with a combination of matte black sphalerite, white cerussite and typical brownish pyromorphite (AESS).

At Alston Moor, Eden, Cumbria, England, UK, sphalerite is associated with ankerite and fluorite (SY p172)

At the Gregory mine, Ashover, Derbyshire, England, UK, sphalerite is associated with fluorite (RES p102, 103).

At the Odin mine, Castleton, Derbyshire, England, UK, sphalerite is associated with fluorite and baryte (RES p130).

At Millclose mine, Darley Dale, Derbyshire, England, UK, sphalerite is associated with pyrite, fluorite and calcite (RES p93, 95).

At Eyam, Derbyshire, England, UK, sphalerite is associated with calcite, fluorite and galena (RES p117).

At Ladywash mine, Eyam, Derbyshire, England, UK, sphalerite is associated with fluorite and pyrite (RES p120).

At Cloud Hill quarry, Breedon on the Hill, Leicestershire, England, UK, sphalerite is associated with calcite, baryte and chalcopyrite in dolomitised limestone (RES p207).

At Lord Ferrer's mine, Staunton Harold, Ashby-de-la-Zouch, Leicestershire, England, UK, sphalerite is associated with galena, chalcopyrite, calcite, baryte and dolomite (RES p222).

At Barrasford Quarry, Chollerton, Northumberland, England, UK, veins of calcite up to 10 mm wide contain abundant masses of sphalerite up to 20 mm across, accompanied by patches of galena and, more rarely, with chalcopyrite and pyrrhotite (JRS 21.14).

At the Callow Hill quarry, Pontesbury, Shropshire, England, UK, sphalerite has been found in quartz veinstone associated with galena (RES p291).

At Judkins quarry, Nuneaton, Warwickshire, England, UK, sphalerite is associated with baryte and calcite (RES p325).

At Roar Hill, Ballater, Buchan Grampian, Scotland, UK, lead-bearing vein mineralisation was exposed during recent work carried out on an unmetalled vehicle track. A small temporary quarry exposed fluorite-bearing quartz veins and minor wulfenite in light-coloured granite. At a second site, a little further to the west, an oxidised galena-bearing quartz vein was exposed.
Sphalerite occurs as honey-brown crystals and cleavages in partly corroded galena at the track exposure. It is much less common than galena. No zinc-bearing supergene minerals have been found at either site (JRS 22.33).

The Nelly James Mine, Miller Canyon, Miller Peak, Cochise County, Arizona, USA, is a former small surface lead, copper, zinc, gold and silver mine located at an altitude of 7250 feet. Mineralisation is a vein deposit Mindat). The mine is now famous for fluorescent minerals collected from the dumps, including calcite (fluoresces red), hydrozincite (sky blue), powellite (creamy-yellow), smithsonite (crimson red), sphalerite (yellow-orange) and willemite (green).
Sphalerite when fine-grained is colourless to tan in daylight, but when coarsely crystalline it has a shiny metallic lustre and can be brown, silver or almost black. Under longwave UV the response is bright yellow-orange. Some specimens exhibit a delayed fluorescent response and tend to get brighter over a short period of time. Under shortwave UV the response is a weak yellow-orange. Under medium range UV the response is also yellow-orange but with a medium brightness. Sphalerite also exhibits a long-duration sustained luminescence upon removal of the longwave UV source (R&M 97.1.48-56).

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, sphalerite has been found, usually on chalcopyrite but sometimes on quartz crystals, and associated with baryte and gypsum (R&M 95.1.87-88).

At the Philadelphia mine, Arkansas, USA, smithsonite pseudomorphs after sphalerite have been found with dolomite (KL p170).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, sphalerite crystals have been found in massive rhodochrosite associated with perloffite. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.515).

At Jopline, Missouri, USA, tetragonal crystals of chalcopyrite have been found epitaxial on sphalerite (FM 47452).

At the PC Mine, Cataract Mining District, Jefferson county, Montana, USA, sphalerite occurred as gemmy green or brown crystals to 23 cm, with the largest crystal weighing 3.2 kilograms (R&M 96.6.494-496).

At Cookes Peak mining district, Luna county, New Mexico, USA, sphalerite was the principal source for zinc in secondary smithsonite. Unoxidised masses occur most often with pyrite and galena in replacement pods in dolomite (R&M 94.3.236).

At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the pegmatites are beryl-type rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most complex zonation and diverse mineralogy of any of the Keyes pegmatites. Six zones are distinguished, as follows, proceeding inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to 1.2 meters in size that were altered to vuggy albite-muscovite with fluorapatite crystals. This unit presumably was the source of the albite, muscovite, fluorapatite, quartz and other crystallised minerals found in pieces of vuggy albite rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including tourmaline, graftonite, triphylite, vivianite, pyrite, pyrrhotite, and beryl crystals to 30.5 cm long and 12.7 cm across.
A 7-mm patch of lustrous black sphalerite embedded in massive triphylite with microsized hureaulite and phosphosiderite or strengite crystals has been collected at the Keyes No. 1 mine (R&M 97.4.325).

At the Big Chief Mine, Glendale, Keystone Mining District, Pennington county, South Dakota, USA, sphalerite occurs with arsenopyrite and quartz (R&M 49.7-8.435-438).

The Purple Diopside Mound, Rose Road, Pitcairn, St. Lawrence county, New York, USA, is situated in marble. The development of veins of large crystals probably occurred as a result of fluid penetration from a concurrent intrusion. Many of the minerals of interest to collectors formed during this primary event, with additional species resulting from the subsequent alteration of scapolite. There seems to be little, if any, secondary, late-stage mineralisation present.
Sphalerite occurs as dark brown submillimetre grains that are spatially associated with corundum (R&M 96.6.552).

Alteration

Sphalerite is a paramorph of wurtzite. The transition from sphalerite to wurtzite occurs around 1020oC.

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + H2O → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4

The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + H2O → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent; it attacks sphalerite as below:

sphalerite, ferric sulphate and water to zinc sulphate, ferrous sulphate and sulphuric acid
ZnS + 4Fe2(SO4)3 + 4H2O → ZnSO4 + 8FeSO4 + 4H2SO4
(AMU/b3-3-7.htm)

skinnerite and sphalerite = Zn-tetrahedrite and chalcocite
4Cu3SbS3 + 2ZnS → Cu10Zn2Sb4S13 + Cu2S
(CM 28.725-738)

sphalerite to covellite: Because covellite is less soluble than sphalerite, supergene covellite may form below the zone of oxidation when dissolved copper ions Cu2+ replace zinc ions Zn2+ from sphalerite.
Cu2+ + sphaleritecovellite + Zn2+
Cu2+ + ZnS → CuS + Zn2+
(KB p527)

Zn-tetrahedrite to chalcocite, antimony, sphalerite and sulphur
Cu10Zn2Sb4S13 → 5Cu2S + 4Sb + 2ZnS + 3S2
(CM 28.725-738)

Zn-tetrahedrite to skinnerite, antimony, sphalerite and sulphur
3Cu10Zn2Sb4S13 → 10Cu3SbS3 + 2Sb + 6ZnS + 3/2S2
(CM 28.725-738)

Zn-tetrahedrite to skinnerite, stibnite and sphalerite
3Cu10Zn2Sb4S13 → 10Cu3SbS3 + Sb2S3 +6ZnS
(CM 28.725-738)

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