Hemimorphite
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| Hemimorphite | |
|---|---|
| Missing image Hemimorphite_Mexico.jpg Hemimorphite from Mapimi, Durango, Mexico. | |
| General | |
| Category | Mineral |
| Chemical formula | Zn4Si2O7(OH)2·H2O |
| Identification | |
| Colour | White, blue, greenish |
| Crystal habit | Polar crystals, with different or hemimorphic ends. Also coxcomb masses, mammillary, stalactitic, or massive. |
| Crystal system | Monoclinic |
| Cleavage | Perfect |
| Fracture | Uneven to conchoidal |
| Mohs Scale hardness | 4.5-5 |
| Luster | Vitreous, silky |
| Refractive index | Transparent to translucent |
| Pleochroism | None |
| Streak | None |
| Specific gravity | 3.516 - 3.525 |
| Fusibility | ? |
| Solubility | Soluble in acid |
| Major varieties | |
| None | |
Hemimorphite, is a sorosilicate mineral which has been mined from days of old from the upper parts of zinc and lead ores, chiefly associated with smithsonite. It was often assumed to be the same mineral and both were classed under the same name of calamine. In the second half of the 18th century it was discovered that there were two different minerals under the heading of calamine - a zinc carbonate and a zinc silicate, which often closely resembled each other.
The silicate was the more rare of the two, and was named hemimorphite because of the hemimorph development of its crystals. This unusual form, which is typical of only a few minerals, means that the crystals are terminated by dissimilar faces. Hemimorphite most commonly forms crystalline crusts and layers, also massive, granular, rounded and reniform aggregates, concentrically striated, or finely needle-shaped, fibrous or stalactitic, and rarely fan-shaped clusters of crystals.
Occurrence
Hemimorphite most frequently occurs as the product of the oxidation of the upper parts of sphalerite bearing ore bodies, accompanied by other secondary minerals which form the so-called iron cap or gossan. Hemimorphite is an important ore of zinc and contains up to 54.2% of the metal.
The regions on the Belgian-German border are well known for their deposits of hemimorphite of metasomatic origin, especially Vieille Montagne in Belgium and Aachen in Germany. Other deposits are near Tarnovice in upper Silesia, Poland; near Phoenixville, Pennsylvania; the Missouri lead-zinc district; Elkhorn, Montana; Leadville, Colorado; and Organ Mountains, New Mexico in the United States; and in several localities in North Africa. Further hemimorphite occurrences are in Nerchinsk, Siberia; Rabelj, Slovenia; Bleiberg, Carinthia, Austria; Matlock, Derbyshire, England.
References
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0471805807
- Mineral galleries (http://mineral.galleries.com/minerals/silicate/hemimorp/hemimorp.htm)
- Webmineral (http://webmineral.com/data/Hemimorphite.shtml)
- Mindat.org (http://www.mindat.org/min-1860.html)