Barstowite

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Barstowite
Barstowite-90280.jpg
Colorless, needle-like barstowite from the Passa Limani slag dump, Lavrio , Attica, Greece (image width 4 mm)
General and classification
other names

IMA 1989-057

chemical formula
  • Pb 4 (CO 3 ) Cl 6 • H 2 O
  • Pb 4 [Cl 6 | CO 3 ] • H 2 O
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.DC.95 ( 8th edition : V / E.08)
01/12/07/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / m (No. 11)Template: room group / 11
Lattice parameters a  = 16.66  Å ; b  = 9.20 Å; c  = 4.20 Å
β  = 91.8 °
Formula units Z  = 2
Physical Properties
Mohs hardness 3 (VHN 100 = 108–117; average 111)
Density (g / cm 3 ) measured: 5.50 to 5.69; calculated: 5.77
Cleavage imperfect according to the prism
Break ; Tenacity uneven; brittle
colour colorless, white
Line color White
transparency transparent to opaque
shine Diamond luster

Barstowite is a very rarely occurring mineral from the mineral class of the " halides " (formerly carbonates , nitrates and borates ). It crystallizes in the monoclinic crystal system with the chemical composition Pb 4 (CO 3 ) Cl 6 · H 2 O and is therefore chemically seen a hydrous lead - Carbonate - Chloride .

Barstowite develops needle-like crystals up to about two centimeters in length, which are usually arranged in weakly parallel mineral aggregates . The individual crystals are transparent and colorless and their surfaces have a diamond-like sheen . However, due to multiple refraction due to the often polycrystalline formation, it usually appears opaque white.

Etymology and history

The mineral was named after the mineral collector and dealer Richard William Barstow (1947-1982) from Cornwall, whose collection is now part of the Museum of Plymouth .

Was first discovered barstowite in a lead- and antimony-containing transition - deposit type outcrop of Bounds Cliff on the south end near St. Endellion in the English county of Cornwall described in 1991, by Chris J. Stanley , GC Jones, Alan D. Hart , Paul Keller and David Lloyd.

Type material of the mineral is kept in the Natural History Museum (register no. 1990,25 and E.1353) and in the archive of the University of Stuttgart , "Mineralogical Collection Prof. Keller" (catalog no. TM-89.57 / 0 / 824- s27 / 2)

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , barstowite still belonged to the mineral class of "carbonates, nitrates and borates" and there to the department of "hydrous carbonates with foreign anions ", where together with ankylite- (Ce ) , Ankylit- (La) , Calcioankylit- (Ce) , Calcioankylit- (Nd) , Dresserit , Dundasit , Gysinit- (Nd) , Hydrodresserit , Kamphaugit- (Y) , Kochsándorit , Montroyalit , Niveolanit , Petterdit , Strontiodresserit and Thomasclarkit- (Y) the "Ankylit group" with the system no. V / E.08 formed.

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 barstowite to the class of "halides" and there to the department of "oxyhalides, hydroxyhalides and related double halides" . This is further subdivided according to the predominant cations (metals) in the compound , so that the mineral can be found according to its composition in the sub-section "With Pb (As, Sb, Bi) without Cu", where it is the only member of the unnamed group 3.DC.95 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the barstowite to the class of "halides" and there in the department of "halide compounds". Here he is the only member of the unnamed group 01/12/07 within the sub-section “Halide compounds with various anions”.

Crystal structure

Barstowite crystallizes monoclinically in the space group P 2 1 / m (space group no. 11) with the lattice parameters a  = 16.66  Å ; b  = 9.20 Å; c  = 4.20 Å and β = 91.8 ° as well as two formula units per unit cell . Template: room group / 11

Education and Locations

Barstowite is a secondary mineral that forms either as a natural reaction product of seawater with metal-containing ore veins and in slag heaps created by anthropogenic influence . In Tunisia, barstowite was also created as a corrosion product on objects containing lead, which were found in 1907 in a shipwreck from the late Hellenistic period off the coast of Mahdia .

At its type locality Bounds Cliff in Cornwall (England), which so far (as of 2014) is also the only known site in the United Kingdom , the mineral entered paragenesis with cerussite , chalcopyrite , dolomite , galena , jamesonite , phosgenite , pyrite , sphalerite and quartz on.

In Austria, barstowite was found near the town of Rattenberg and in an old slag dump near St. Gertraudi (municipality of Reith im Alpbachtal) in Tyrol.

Other known sites (as of 2014) are the ancient slag heaps "Passa Limani" and "Vrissaki" near Lavrio in the Greek region of Attica , some slag heaps in the vicinity of Campiglia Marittima and Piombino in the Italian region of Tuscany , in a lead-zinc Pit at Kayrakty (Kairakty) in the Karagandy Oblysy area of Kazakhstan.

See also

literature

  • CJ Stanley, GC Jones, AD Hart, P. Keller, D. Lloyd: Barstowite, 3PbCl 2 · PbCO 3 · H 2 O, a new mineral from Bounds Cliff, St Endellion, Cornwall . In: Mineralogical Magazine . tape 55 , 1991, pp. 121–125 ( rruff.info [PDF; 629 kB ; accessed on June 11, 2018]).
  • LM Steele, JJ Pluth, CJ Stanley: Crystal structure of barstowite (3PbCl 2 · PbCO 3 · H 2 O) . In: Mineralogical Magazine . tape 63 , no. 6 , December 1999, pp. 901-907 ( minersoc.org [PDF; 1.6 MB ; accessed on June 11, 2018]).

Web links

Commons : Barstowite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; March 2014 (PDF 1.5 MB)
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  179 .
  3. ↑ a b c d Barstowite . 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; 68  kB ; accessed on June 11, 2018]).
  4. ↑ John L. Jambor : New Mineral Names . In: American Mineralogist . tape  77 , 1992, pp. 670–675 ( minsocam.org [PDF; 715 kB ; accessed on June 11, 2018]).
  5. ↑ CJ Stanley, GC Jones, AD Hart, P. Keller, D. Lloyd: Barstowite, 3PbCl 2 · PbCO 3 · H 2 O, a new mineral from Bounds Cliff, St Endellion, Cornwall . In: Mineralogical Magazine . tape 55 , 1991, pp. 122 ( rruff.info [PDF; 629 kB ; accessed on June 11, 2018]).
  6. ↑ CJ Stanley, GC Jones, AD Hart, P. Keller, D. Lloyd: Barstowite, 3PbCl 2 · PbCO 3 · H 2 O, a new mineral from Bounds Cliff, St Endellion, Cornwall . In: Mineralogical Magazine . tape 55 , 1991, pp. 121–125 ( rruff.info [PDF; 629 kB ; accessed on June 11, 2018]).
  7. ^ Type mineral catalog of the University of Hamburg - Barstowit
  8. ↑ Mindat - Late-Hellenistic shipwreck site, Mahdia, Mahdia Governorate, Tunisia
  9. ↑ Find location list for barstowite at the Mineralienatlas and at Mindat