Hemimorphite

hemimorphite

rosasite

cerussite

smithsonite

Images

Formula: Zn4(Si2O7)(OH)2.H2O
Sorosilicate (Si2O7 groups)
Crystal System: Orthorhombic
Specific gravity: 3.475 measured, 3.484 calculated
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, pale blue, pale green, gray, brown
Solubility: Slightly soluble in hydrochloric acid
Common impurities: Cu,Fe
Environments:

Hydrothermal environments

Hemimorphite is one of the three main supergene zinc minerals, the others being smithsonite and hydrozincite. Hemimorphite is a high temperature secondary mineral found in the oxidation portion of zinc deposits, associated with smithsonite, sphalerite, cerussite, anglesite and galena.

Localities

At the Nakhlak Mine, Anarak District, Nain County, Isfahan Province, Iran, epigenetic (formed later than the surrounding or underlying rock formation) vein deposits and metasomatic replacement bodies are hosted by a chalky Upper Cretaceous (100.5 to 66 million years ago) limestone. The limestone underwent dolomitisation prior to sulphide mineralisation. The principal primary ore mineral is galena, associated with minor or trace amounts of sphalerite, tetrahedrite -tennantite, pyrite and chalcopyrite as inclusions. The main secondary ore mineral is cerussite, sometimes associated with minor amounts of anglesite, plattnerite, wulfenite, minium, mimetite, covellite, chalcanthite, malachite and goethite. Many trace elements are present in the primary galena, but most notably it is rich in silver and antimony and poor in bismuth.
Specimens have been collected that show what appear to be typical, pale blue botryoidal crusts of hemimorphite partially covered by cerussite crystals (Minrec 54.3.383-408).

At Mapimi, Mexico, fluorellestadite pseudomorphs after hemimorphite have been found (KL p222).

At the Ojuela Mine, Mapimí, Mapimí Municipality, Durango, Mexico, hemimorphite occurs with rosasite (Mindat photos).
In 2020 remarkable intense blue hemimorphite crystals to 8 cm long were found here. The blue colour was due to a surface coating that was found to contain phthalocyanine blue BN. This pigment does not occur in nature, so the blue colour of the hemimorphite must be anthropogenic (R&M 97.2.177).
Hemimorphite from thr Ojuela Mine - Image

At Roughton Gill, Caldbeck Fells, Cumbria, England, UK, hemimorphite is relatively common as radiating sprays of millimetre-sized platy crystals, which are occasionally associated with chrysocolla, aurichalcite, rosasite and in one case mottramite (JRS 11.14).

At the Roughton Gill mine, At Roughton Gill, Caldbeck Fells, Cumbria, England, UK, fine specimens of blue botryoidal hemimorphite occur. Rosasite is a common associate, but the botryoidal forms are not usually coated with other minerals beyond a little pyromorphite (JRS 14.13-14).
Hemimorphite from the Roughton Gill Mine - Image

At the Golconda mine, Brassington, Derbyshire, England, UK, hemimorphite has been found on baryte (RES p107).
Hemimorphite grom the Golconda Mine - Image

At the Millclose mine, Darley Dale, Derbyshire, England, UK, hemimorphite occurs on baryte and on calcite (RES p98).
Hemimorphite from the Millclose Mine - Image

At the Wapping mine, Matlock Bath, Derbyshire, England, UK, hemimorphite occurs on fluorite, sometimes with minor baryte or limonite (RES p72).
Hemimorphite from the Wapping Mine - Image

At Joplin, Missouri, USA, hemimorphite pseudomorphs after calcite have been found (KL p225).
Hemimorphite from Joplin - Image

At the Tintic Mining District, Juab County, Utah, USA, hemimorphite has been found, mostly from the mines in the Mammoth area, as well as from the Centennial Eureka and Minnie Moore mines. Commonly, hemimorphite is associated with rosasite, aurichalcite and calcite, but it also occurs alone on a matrix of quartz. Single crystals up to 1 cm in size are known, but the mineral usually occurs as bundles or druses of crystals. Hemimorphite here is almost always colourless and transparent to white, but some interesting blue crystals on scalenohedral calcite crystals were found on the upper dumps of the North Star mine (MinRec 55.2.205-206).
Hemimorphite from Tintic - Image

At the Kabwe mine, Central Province, Zambia, hemimorphite is common though often inconspicuous. It occurs mainly as intergrowths with cerussite and goethite, and it has been found associated with tarbuttite and smithsonite, and also with zincolibethenite on a limonite matrix (R&M 94.2.125-126).
Hemimorphite from Kabwe - Image

Alteration

The first stage in the formation of zinc supergene minerals is the oxidation of sphalerite to zinc sulphate, which is very soluble and remains in solution as zinc and sulphate ions:
ZnS + 2O2 → Zn2+ + SO42-
Hemimorphite forms only at high pH (very alkaline conditions), when Zn2+ ions in solution react with a mobile source of silicate ions, such as silicic acid, normally derived from the weathering of silicate minerals. Hemimorphite is therefore most abundant in areas where such a source exists, such as the Askrigg block of the Northern Pennine Orefield, UK, where there are numerous beds of chert (JRS 18.14).

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