Hemimorphite - Encyclopedia

    Class : Silicates
    Subclass : Sorosilicates
    Crystal system : Orthorhombic
    Chemistry : Zn4Si2O7(OH)2 . H2O
    Rarity : Common

Hemimorphite is a secondary silicate of zinc present in the oxidation zones of lead and zinc sulphide deposits. It is particularly common in arid climate and clay-marl context where it is the main oxidized zinc ore, which can form entire hills. The "calamine" of the former miners is essentially hemimorphite, more rarely smithsonite. The hemimorphite owes its name to the Greek hêmi (half) and morphê (form) because its doubly-terminated crystals have 2 different terminations due to the absence of center of symmetry. Hemimorphite generally exists in concretions, stalactites or in botryoidal masses, evoking smithsonite, also sometimes in rocky or earthy masses, cavernous, brown in color due to iron oxides ; it is a mineral that "rings" and disintegrates into thin scales. The crystals are fairly common, flattened to lamellar, rarely centimetric, elongated and streaked vertically and often grouped in fans. As with wulfenite, crystal shpe depend on acidity and oxidation-reduction conditions. Hemimorphite is colorless to white, sometimes green, pale blue or yellowish brown, when it is colored by iron oxides. Hemimorphite was once an occasional zinc ore nowadays supplanted by sphalerite.

Blue hemimorphite from Malipo Mine, Wenshan Co., Yunnan, China

Blue hemimorphite from Malipo Mine, Wenshan Co., Yunnan, China

Hemimorphite on siderite from Peyrebrune, Tarn, France

Blue hemimorphite from M'Fouati, Congo

Hemimorphite in the World

Clear crystals of 4 cm, assembled in splendid groups lining cavities of limonite were discovered in the Aquiles Serdan mines in Mexico. Also in Mexico, the Ojuela mine near Mapimi provided 7.5 cm white crystals. The Franklin Mine in New Jersey has produced clear, colorless to white groups of rosettes of up to 10 cm in diameter. Massive hemimorphite is common and has also yielded incredible discoveries. At the Chah-Kuh mine (Iran), the mine excavated gigantic geodes with mounded concretions more than 50 cm in diameter; comparable weights were exploited at Broken Hill (Zambia) and the state of Zacatecas (Mexico). The M'Fouati deposit in the Congo also produced beautiful crystals (main photo) as well as botryoidal masses of a deep blue. More recently, China (Malipo Mine, Wenshan) has produced sumptuous sky-blue masses.

Hemimorphite in France

In France, the best specimens are bluish crystals up to 2 cm frequently grouped in rosettes. Inlaid incrustations of a very beautiful blue color come from the Bentillou mine (Seintein, Ariège) but also from Germs-sur-l'Oussouet (Haute-Pyrénées). It is found in millimetric crystals in Argentolles, Mechelen (Gard), Can Pei (Pyrenees-Orientales), Peyrebrune (Tarn) where the sprays can reach half a centimeter, Propières and Longefay (Rhône), Argentolle (Saône-et-Loire), etc ...


Rare twinning on {101} only.

Fakes and scams

Some Mexican hemimorphite crystals are dyed in blue with phthalocyanine. The dye penetrates preferentially into fractures and surface roughness, in appearance these hemimorphites resemble stilbites covered with Indian cavansite. Photos Mardani Fine Minerals.

Hardness : 4.5 to 5
Density : 3,475
Fracture : Irregular to sub-onchoidal
Streak : White

TP : Translucent to transparent
RI : 1.614 to 1.636
Birefringence : 0.022
Optical character : Biaxial +
Pleochroism : Very weak
Fluorescence : Yellow, white, green

Solubility : Acids

Magnetism : None
Radioactivity : None


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