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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:
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
In Hunan, China, hemimorphite has been found as indistinct sprays of turquoise to white crystals, to 1 cm
(AESS).
Hemimorphite from Hunan - Image
At Shangri-La County, Dêqên Autonomous Prefecture, Yunnan, China, with turquoise coloured hemimorphite occurs lining
cavities in a brown limonite matrix
(AESS).
Hemimorphite from Shangri-La County - Image
At Wenshan Mine, Wenshan City, Wenshan, Yunnan, China, fine specimens of brightly coloured blue hemimorphite have been
found
(AESS and Mindat photos)
Hemimorphite from Wenshan - Image
At the Birrity quarry, Arbouet-Sussaute, Bayonne, Pyrénées-Atlantiques, Nouvelle-Aquitaine, France,
hemimorphite has been found with calcite
(Mindat photo).
Hemimorphite from the Birrity Quarry -
Image
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 the 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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