Phosgenite

• Cromfordit

Phosgenite, interchangeably also known as Cromfordit or Kerasin or under its mining designations Bleihornerz or horn lead, is a rarely occurring mineral from the mineral class of " carbonates and nitrates ." It crystallizes in the tetragonal crystal system with the chemical composition Pb2 [ Cl2 | CO3 ] and developed mostly short to long prismatic or tabular crystals, but also granular to massive mineral aggregates, either white colorless to or by foreign admixtures of white yellow, light pink, greenish or brownish yellow to brown in color may be.

Special Features

Phosgenite occasionally shows weak yellow-orange fluorescence under short-and long-wave UV light.

Etymology and history

As a first description of the Phosgenits applies from 1841 by August Breithaupt ( 1791-1873 ), who named the mineral because of its composition, the chemical compound phosgene. However, it is possible that the first description already took place in 1800 by Dietrich Ludwig Gustav Karsten, the (, First Edition, Berlin: 78) is in the " Mineralogical Tables," described as " horn lead ," but probably not recognized as a separate mineral.

Already in 1785 was Charles Grenvill (after Bridges and Smith, 1983) in England, more precisely discovered in the " Bage Mine" at Cromford in Derbyshire, a mineral that was first seen as a new mineral species and was named after its type locality as Cromfordit. Later, however, it turned out that it was Phosgenite.

Classification

In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th edition ) of the Phosgenite belongs to the department of " outdoor water carbonates with foreign anions ." The new Strunz'sche Mineral classification divided here but now more specific to the nature of the cations and the mineral is found in accordance with the subdivision " with lead ( Pb) and bismuth ( Bi) ".

The more commonly used in English-speaking classification of minerals according to Dana represents the Phosgenite in the class of " carbonates, nitrates and borates " and there is the only mineral of the unnamed group " 16a.03.04 " in the department of " carbonates with hydroxyl or halogen, and the general formula ( AB) 2 (XO) 3Zq ".

Education and Locations

Phosgenite is a typical secondary mineral and is formed as a transformation product of galena (PbS ) carbonated or chlorine under the action of water such as sea water in the oxidation zone of lead deposits. It takes place there in paragenesis with cerussite, anglesite, matlockite, Laurionite and other secondary lead minerals.

So far Phosgenite was at 122 localities demonstrated ( of 2009), so among other things in Catamarca (Argentina ); in Apollyontal (New South Wales), at Mount Isa (Queensland ), at Dundas in Tasmania and Coppin Pool ( Western Australia ) in Australia; Pará and São Paulo in Brazil; Hesse, Lower Saxony, North Rhine -Westphalia and Rhineland -Palatinate in Germany; some regions of France; in the Greek of Attica; England (Cornwall, Derbyshire ), Scotland ( Grampian Mountains ) and Wales ( Ceredigion, Gwynedd ) in the UK; in Sardinia and other regions in Italy; at Tsumeb in Namibia; Alteck and High Sonnblick in Austria; in Tarnów Góra in Poland; in the Russian Altai Mountains; as well as many regions of the United States.

Crystal structure

Phosgenite crystallized tetragonal in the space group P4/mbm ( Raumgruppen-Nr. 127) with the lattice parameters a = 8.16 Å and c = 8.88 Å and four formula units per unit cell.

Use

As a pigment and medicine

In the chemical analysis of various cosmetics and eyeshadow of the Ancient Egyptians also Gemenganteile of Phosgenite and Laurionite were found unusually. Both minerals are predominantly white and are rarely found in nature. Experiments proved that the compounds with little effort even though time-consuming can be synthesized even at room temperature. The researchers examined the presumption that the use of reason could not have been alone to set the desired color make-up, as this would have been easier to accomplish through the use of abundant naturally occurring Cerussits.

In ancient texts of Pliny the Elder and Dioscorides Pedanios is to read that the powder produced was made ​​into a kind of eye drops or to mask skin spots on the face of the women. Even in Roman times these substances have been used for therapeutic, preventive health and cosmetic purposes.

As a gemstone

For commercial use as a gemstone of Phosgenite with a Mohs hardness of only 2 to 3 is too soft and too rare. As collector's items they are still like ground of amateur or professional grinders in facet shape.