Alamosit

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Alamosit
Alamosite-Leadhillite-Melanotekite-ea6b.jpg
Alamosite (colorless) and Melanotekit (black) on leadhillite from Tsumeb , Namibia (size: 3.5 cm × 2.5 cm × 1.5 cm)
General and classification
other names

Lead silicate

chemical formula
  • PbSiO 3
  • Pb 12 [Si 12 O 36 ]
  • Pb 3 [Si 3 O 9 ]
Mineral class
(and possibly department) 		Silicates and germanates - chain and band silicates
System no. to Strunz
and to Dana 		9.DO.20 ( 8th edition : VIII / F.32)
65.07.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 / c (No. 13)Template: room group / 13
Lattice parameters a  = 11.23  Å ; b  = 7.08 Å; c  = 12.95 Å
β  = 119.6 °
Formula units Z  = 1
Physical Properties
Mohs hardness 4.5
Density (g / cm 3 ) measured: 6.488 (3); calculated: [6.30]
Cleavage completely after {010}
colour colorless, white, light gray to beige
Line color White
transparency transparent to translucent
shine Diamond luster
Crystal optics
Refractive indices n α  = 1.947
n β  = 1.961
n γ  = 1.968
Birefringence δ = 0.021
Optical character biaxial negative
Axis angle 2V = measured: 65 °; calculated: 70 °

Alamosit is a seldom occurring mineral from the mineral class of " silicates and germanates " with the chemical composition PbSiO 3 and thus, chemically speaking, a lead silicate that structurally belongs to the chain silicates .

Alamosit crystallizes in the monoclinic crystal system and develops fibrous crystals with a diamond-like sheen on the surfaces, which are usually arranged in radial to spherical mineral aggregates up to about 7.5 centimeters in size. In its pure form, Alamosit is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a light gray to beige color, the transparency decreasing accordingly.

Etymology and history

Alamosite was first discovered near the city of Álamos ( Alamos ) in the Mexican state of Sonora and described in 1909 by Charles Palache and Herbert E. Merwin , who named the mineral after its type locality .

Type material of the mineral is registered at Harvard University in Cambridge (Massachusetts) in the USA under the register no. 84859 and 85509 kept.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the alamosite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it was named after the "alamosite group" the system no. VIII / F.32 and the other member Aerinit .

The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies alamosite in the category of "chain and band silicates (inosilicates)". However, this is further subdivided according to the structure of the chains, so that the mineral can be found according to its composition in the subsection “Chain and band silicates with 7-, 8-, 10-, 12- and 14-periodic chains”, where it can be found forms the unnamed group 9.DO.20 as the only member .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns alamosite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here he is to be found as the only member of the unnamed group 65.07.01 within the sub-section “ Chain silicates: Simple unbranched chains, W = 1 with chains P> 7 ”.

Crystal structure

Crystal structure of alamosite

Alamosit crystallizes monoclinically in the space group P 2 / c (space group no. 13) with the lattice parameters a  = 11.23  Å ; b  = 7.08 Å; c  = 12.95 Å and β = 119.6 ° as well as one formula unit per unit cell . Template: room group / 13

The crystal structure of alamosite consists of SiO 4 - tetrahedra that are (010) connected to unbranched, zig-zag Twelve single chains perpendicular to the b-axis. These are linked to one another via PbO 3 and PbO 4 pyramids to form layers along the same axis.

The crystal forms although those closely related by wollastonite , but by the much larger Pb 2+ - ion is not directly comparable.

Education and Locations

Alamosite (colorless) with inclusions of an unknown, orange-colored mineral and melanotekit (black) from Tsumeb, Namibia (size: 1.9 cm × 1.9 cm × 1.5 cm)

Alamosite formed secondarily in the oxidation zone of lead-containing ore - deposits . As accompanying minerals may include Anglesite , Cerussite , Diaboleit , Fleischerit , hematite , Kegelit , Leadhillit , Melanotektit , Phosgenite , Shattuckit , Wickenburgit , Willemit , Wulfenit occur.

As a rare mineral formation, alamosite could only be detected at a few localities, whereby so far (as of 2014) fewer than 15 localities are known. In addition to its type locality Alamos in Sonora, the mineral was also found in Mexico in the San Pascual Mine (San Pasquale Mine) near Zimapán in the state of Hidalgo .

Other previously known sites are the Tsumeb Mine (Tsumcorp Mine) in Namibia, the Skjerpemyr Mine in the mining district of Grua (Oppland), the Harstigen Mine near Pajsberg and the Långban mining community in the Swedish province of Värmland and the Lucky Cuss Mine near Tombstone , the Evening Star Mine at Tiger Wash (Belmont Mountain, Maricopa County ), several small sites in the Artillery Mountains ( Mohave County ) and the Mammoth-Saint Anthony Mine in the St. Anthony deposit (Mammoth District, Pinal County ) in the US state of Arizona .

See also

literature

  • Charles Palache , Herbert E. Merwin : Alamosite, a new lead silicate from Mexico . In: American Journal of Science . tape 27 , 1909, pp. 399–401 ( rruff.info [PDF; 95 kB ; accessed on October 31, 2017]).
  • ML Boucher, PR Donald: The crystal structure of alamosite, PbSiO 3 . In: Journal of Crystallography . tape 126 , 1968, pp. 98–111 ( rruff.info [PDF; 738 kB ; accessed on October 31, 2017]).
  • Sergey V. Krivovichev, Peter C. Burns: Crystal structure of synthetic alamosite Pb [SiO 3 ] . In: Zapiski Vserossijskogo Mineralogicheskogo Obshchestva . tape 133 , no. 5 , 2004, p. 70–76 ( rruff.info [PDF; 418 kB ; accessed on October 31, 2017] in Russian with a brief description in English).

Web links

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

Individual evidence

  1. ↑ a b c Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  736 (first edition: 1891).
  2. ↑ a b IMA / CNMNC List of Mineral Names; September 2017 (PDF 1.67 MB)
  3. ↑ 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.  653 .
  4. ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  540 .
  5. ↑ a b c d Alamosite . 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; 65  kB ; accessed on October 31, 2017]).
  6. ↑ a b c d e Mindat - Alamosite
  7. ^ Charles Palache , Herbert E. Merwin : Alamosite, a new lead silicate from Mexico . In: American Journal of Science . tape  27 , 1909, pp. 399–401 ( rruff.info [PDF; 95 kB ; accessed on October 31, 2017]).
  8. ↑ Mindat - Number of localities for Alamosit
  9. ↑ Find location list for Alamosit in the Mineralienatlas and Mindat