Smithsonite

• Noble calamine or Edelgalmei
• Kohlengalmei
• Calamine

Smithsonite, outdated also known as smithsonite, calamine called noble or Edelgalmei and as a chemical compound of zinc carbonate, is a rarely occurring mineral from the mineral class of carbonates. It crystallizes in the trigonal crystal system with the chemical composition of Zn [ CO3 ] and usually develops rhombohedral crystals, but also racemose, stalactitic or massive aggregates in mostly blue or green color. Also colorless, white, light yellow or brown crystals are known.

Special Features

Pure Smithsonite is colorless. However, it may be differently colored by incorporation of additional ions into the crystal system. For example, the bluish color is caused by foreign admixtures of copper ions and the pink to purple color with cobalt ions.

The crystals of Smithsonite are translucent, transparent, and less frequently point to the crystal faces glass to pearly. With a Mohs hardness of 4-5 and a specific gravity of 4.0 to 4.65, it is quite soft and lightweight mineral with a zinc content of up to 64.8 %. However, zinc can be replaced diadoch ( equivalent) by iron, manganese, magnesium, calcium, rare lead or cadmium. Frequently Smithsonite is contaminated with iron oxide and aluminum silicate.

Intense heating Smithsonite decomposes to zinc oxide. This decay was formerly used among other things for the qualitative detection: on charcoal before the blowpipe is sublimed zinc oxide is deposited. This is when hot lemon yellow (see also Zinksuboxide ) and decreases only when cooled to the typical white color of the zinc oxide.

On several shows Smithsonite green, blue and white, pink or brown fluorescence.

Etymology and history

The mineral was named in honor of the well-known English mineralogist James Smithson ( 1765-1829 ).

As calamine (also calamine ) a mixture of smithsonite and hemimorphite ( Kieselzinkerz ) or additionally designated Hydrozincite.

Classification

In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th edition ) of the Department of Smithsonite is assigned to " anhydrous carbonates without foreign anions ." The new Strunz'sche Mineral classification divided here but even more precisely on the nature of the cations involved. Since the zinc is involved in a double positive charge in the compound, the mineral is in accordance with the subdivision " alkaline-earth (and other M2 ) carbonates ".

The classification of minerals according to Dana leads the Smithsonite in the subdivision of " anhydrous carbonates with a simple formula A CO3 " where he, together with the crystal chemically similar minerals calcite, magnesite, siderite, rhodochrosite, Sphaerocobaltit, Otavit and Gaspéit the " Calcitgruppe with trigonal symmetry and the space group R3c " forms.

Modifications and varieties

Form particularly iron and manganese -rich varieties, which means species between smithsonite and siderite or rhodochrosite one hand, on the other hand, have been termed Zinkeisenspat, Eisenzinkspat and Manganzinkspat.

Education and Locations

Smithsonite is formed by oxidation in the Descendant different, primary zinc ore veins. It is found there, mostly in small crystals, common in kidney-shaped, shell aggregates, in stalaktitischen, also rough in dense and earthy masses, forming nests, sticks and storage, especially in calcareous and dolomitic rocks of different formations in space Eschweiler- Stolberg in the Rhineland in Wiesloch in Baden, as a coating on calcite crystals in the Rammelsberg near Goslar / Harz, in Tarnowitz in Silesia, also in Carinthia, Styria, Belgium ( led here to the political curiosity Neutral Moresnet ), England, on the island of Thassos in Greece. Smaller deposits were mined in Germany in the 19th century in the room Iserlohn, Brilon ( in the 17th century ) and Inzell ( Bavaria).

Other localities include Broken Hill in Australia, Tsumeb in Namibia, Magdalena / New Mexico in the United States. Worldwide, so far (as of 2009) about 1600 known localities.

Crystal structure

Smithsonite crystallizes in the trigonal crystal system in space group R3c with lattice parameters a = 4.6528 Å and c = 15.025 Å and six formula units per unit cell.

Smithsonite is isostructural with calcite.

Use

As a raw material

Smithsonite is an important zinc ore and until the end of the 18th century indispensable as the only possible raw material for the manufacture of brass. The usual procedure at this time for making brass was the cementation, in which the " calamine " could be added directly as an additive to the piece of copper and did not have to be processed only to pure zinc. This was referred to as a " dutch style " of brass manufacturing. However, one first recognized a long time not that calamine afforded the zinc required for the brass, but took him for a kind of dye that colored the red copper golden.

As a gemstone

Although Smithsonite is one of the gems rather little-known due to its relative softness. However, he is due to its appealing blue-green to purple color and his occasionally iridescent pearlescence quite sought after and is processed according to jewelery or as tumbled stone to so-called " Handschmeichlern ". Since Smithsonite is predominantly found in translucent aggregates, preferably the cabochon cut is used.

Smithsonite is in appearance the minerals and gemstones Hemimorphite, turquoise, chrysoprase and jade, but also appropriately colored calcites and aragonite similar and partially imitated by them. When buying expensive pieces, therefore, a proof of authenticity should be required.

Ecological Significance

The Galmeiveilchen grows on galmeihaltigen floors, is now very rare, and in contrast to conventional yellow violets. Several Galmeiveilchenfluren stand in the Aachen region under protection.