Phosgenite
| Phosgenite | |
|---|---|
 (comparative scale: 1 "with notch at 1 cm) |
|
| General and classification | |
| other names |
|
| chemical formula | Pb 2 [Cl 2 | CO 3 ] |
|
Mineral class (and possibly department) |
Carbonates and nitrates |
|
System no. to Strunz and to Dana |
5.BE.20 ( 8th edition : V / C.09) 16a.03.04.01 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal; 4 / m 2 / m 2 / m |
| Space group | P 4 / mbm (No. 127) |
| Lattice parameters | a = 8.16 Å ; c = 8.88 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 2 to 3 |
| Density (g / cm 3 ) | measured: 6.12 to 6.15; calculated: 6.124 |
| Cleavage | clear to good according to {001} and {110}; indistinct after {010} |
| Break ; Tenacity | shell-like |
| colour | colorless, gray, white-yellow, light pink, greenish, brownish-yellow to brown |
| Line color | White |
| transparency | transparent to translucent |
| shine | Diamond luster |
| Crystal optics | |
| Refractive indices |
n ω = 2.118 n ε = 2.145 |
| Birefringence | δ = 0.027 |
| Optical character | uniaxial positive |
| Pleochroism | very weak: ω = reddish; ε = greenish |
| Other properties | |
| Special features | occasionally weak yellow-orange fluorescence under short- and long-wave UV light |
Phosgenit , also under its mining designations Bleihornerz or horn lead as well as synonymous Cromfordit or Kerasin or known, a rarely occurring minerals from the mineral class of "carbonates and nitrates" with the chemical composition Pb 2 [Cl 2 | CO 3 ]. The mineral is so chemically seen a lead - carbonate with additional chlorine ions .
Phosgenite crystallizes in the tetragonal crystal system and develops mostly short to long prismatic or tabular crystals , but also granular to massive mineral aggregates with a diamond-like sheen on the surfaces. In its pure form, phosgenite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear translucent white and take on a light pink, greenish, yellowish or brownish-yellow to brown color due to foreign admixtures.
Etymology and history
The first description of phosgenite is that of 1841 by August Breithaupt (1791–1873), who named the mineral after the chemical compound phosgene due to its composition . However, it is possible that the first description was made around 1800 by Dietrich Ludwig Gustav Karsten , who described it as horn lead in the "Mineralogical Tables" (Berlin, First Edition: 78) , but probably did not recognize it as an independent mineral.
As early as 1785, Charles Grenvill (after Bridges and Smith, 1983) in England, more precisely in the "Bage Mine" near Cromford in Derbyshire, discovered a mineral that was initially thought to be a new type of mineral and was named Cromfordite based on its type of locality . However, it later turned out that it was phosgenite.
classification
In the outdated, but still in use 8th edition of the mineral classification according to Strunz , phosgenite belonged to the common mineral class of "carbonates, nitrates and borates" and to the department of "anhydrous carbonates with foreign anions ", where it was named after bismuthite and " Phosgenite-Bismutite-Group “with the system no. V / C.09 and the other members Beyerite and Kettnerite .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns phosgenite to the newly defined class of “carbonates and nitrates”, but also to the department of “carbonates with additional anions; without H 2 O “. This is further subdivided according to the predominant metals in the compound, so that the mineral can be found according to its composition in the sub-section "With lead (Pb) and bismuth (Bi)", where it is the only member of the unnamed group 5.BE .20 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns phosgenite to the class of "carbonates, nitrates and borates" and there to the category of "carbonates - hydroxyl or halogen". Here he is the only member of the unnamed group 16a.03.04 within the subsection “Carbonates - Hydroxyl or Halogen with (AB) 2 (XO) 3 Z q ”.
Crystal structure
Phosgenite crystallizes tetragonally in the space group P 4 / mbm (space group no. 127) with the lattice parameters a = 8.16 Å and c = 8.88 Å as well as 4 formula units per unit cell .
properties
Phosgenite occasionally shows weak yellow-orange fluorescence under short- and long-wave UV light.
Education and Locations
Phosgenit is a typical secondary mineral and formed as a conversion product from galena (PbS) under the action of carbonated or chlorine-containing water such as sea water in the oxidation zone of lead - deposits . It occurs there in paragenesis with cerussite , anglesite , matlockite , laurionite and other secondary lead minerals .
As a rare mineral formation, phosgenite could only be detected in a few places, whereby so far (as of 2016) around 150 sites are known.
In Germany, the mineral has so far appeared on slag heaps near Richelsdorf in Hesse, Astfeld in Lower Saxony and the former municipality of Kall (now Mechernich ) as well as in various mines near Selbeck ( Ratingen ), Velbert , Essen and Marl in North Rhine-Westphalia and Puderbach in Rhineland -Pfalz auf.
In Austria, phosgenite was found on a slag dump near Waitschach (municipality of Hüttenberg) in Carinthia, on slag dumps in the municipality of Kolm-Saigurn in the Hüttwinkl valley ( Hohe Tauern ) and near Schwarzleo in the municipality of Leogang in Salzburg and in the municipality of Oberzeiring in Styria .
Other locations include Argentina, Australia, Brazil, Chile, France, Greece, Iran, Ireland, Italy, Morocco, Mexico, Namibia, Norway, Poland, Russia, South Africa, the Czech Republic, Tunisia, the United Kingdom (UK) and the United States of America (USA).
use
As a pigment and in medicine
During the chemical analysis of various cosmetics and eye make-up by the ancient Egyptians , it was unusual to find mixtures of phosgenite and laurionite . Both minerals are predominantly white and rarely occur in nature. Experiments have shown that the compounds can be produced synthetically at room temperature with little effort, albeit time-consuming. The investigating researchers made the assumption that the reason for use could not have been the setting of the desired make-up color alone, as this would have been easier to achieve through the use of the abundant naturally occurring cerussite .
In ancient texts by Pliny the Elder and Pedanios Dioscurides it can be read that the powder produced was processed into a kind of eye drop or to cover spots on the face of women. In Roman times, too, these substances were used for therapeutic, health-preventive and cosmetic purposes.
As a gem
With a Mohs hardness of only 2 to 3, phosgenite is too soft for commercial use as a gemstone . As collector's items, they are still gladly cut into a facet shape by hobby or professional grinders .
See also
literature
- Dietrich Ludwig Gustav Karsten: Tabular overview of the mineralogically simple fossils [as horn lead]. In: Mineralogical tables Heinrich August Rottmann, Berlin 1800, pp. 50–50
- August Breithaupt: Phosgenites plumbosus shorter phosgenite. In: Complete characteristics of the mineral system. Volume 2, Arnoldische Buchhandlung, Dresden and Leipzig 1841, pp. 183–184 ( 137.7 kB )
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 580 (first edition: 1891).
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 125 .
Web links
- Mineral Atlas: Phosgenite (Wiki)
- RRUFF Database-of-Raman-spectroscopy - Phosgenite (English)
- American-Mineralogist-Crystal-Structure-Database - Phosgenite (English)
Individual evidence
- ↑ Webmineral - Phosgenite
- ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 300 .
- ↑ a b Phosgenites. in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF; 63.5 kB).
- ↑ a b c d Mindat - Phosgenites
- ↑ J. Jones: Mineralogy of Bage Mine . In: Bulletin Peak District Mines Historical Society. Volume 8, No. 4, December 1982 (English, PDF 150.2 kB ( Memento of the original from May 13, 2012 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ).
- ↑ Rocks and Crystals from Derbyshire - Cromfordite ( Memento from August 26, 2004 in the Internet Archive ) (English)
- ↑ Mindat - Number of localities for phosgenites
- ↑ List of locations for phosgenite in the Mineralienatlas and Mindat
- ↑ Make-up of the Egyptians. ( Memento from July 7, 2012 in the web archive archive.today ) - “Archimedes” series on ARTE from July 17, 2001.
- ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 224 .
- ↑ Realgems - Phosgenite (with picture examples of cut stones)
