Laphamite

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Laphamite
Laphamite-91012.jpg
Needle-like clusters of dark yellow laphamite crystals from Burnside , Northumberland County (Pennsylvania) , USA (image width 1.5 mm)
General and classification
other names

IMA 1985-021

chemical formula Ace 2 (Se, S) 3
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.FA.30 ( 8th edition : II / F.02)
11/02/06/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / n (No. 14, position 2)Template: room group / 14.2
Lattice parameters a  = 11.86  Å ; b  = 9.76 Å; c  = 4.27 Å
β  = 90.2 °
Formula units Z  = 2
Physical Properties
Mohs hardness 1 to 2
Density (g / cm 3 ) measured: 4.5 (1); calculated: 4.60
Cleavage completely after {010}
Break ; Tenacity flexible but not elastic; extremely malleable
colour dark red with strong, fiery red inner reflections
Line color Red orange
transparency translucent to opaque
shine Greasy shine

Laphamite is a very rarely occurring mineral from the mineral class of "sulfides and sulfosalts". It crystallizes in the monoclinic crystal system with the chemical composition As 4 (Se, S) 6 or As 2 (Se, S) 3 The elements selenium and sulfur indicated in the round brackets can represent each other in the formula ( substitution , diadochia ), but are always in the same proportion to the other components of the mineral.

Laphamite is translucent to almost opaque and develops tabular to prismatic crystals up to about five millimeters in length of dark red color with strong, fiery red, internal reflections. The crystal surfaces have a fat-like sheen . Laphamit leaves a red-orange line on the marking board .

With a Mohs hardness of 1 to 2, laphamite is one of the soft minerals that, like the reference minerals talc (hardness 1) and gypsum (hardness 2), can be scraped off or scratched with the fingernail.

Etymology and history

Laphamite was first discovered at Burnside in Northumberland County (Pennsylvania) of Pennsylvania in the United States of America and described in 1986 by Pete J. Dunn , Donald R. Peacor , Alan J. Criddle and Robert B. Finkelman , who named the mineral after the earlier Chief mineralogists of the "Pennsylvania Geological Survey" named Davis M. Lapham (1931–1974).

Type material of the mineral is kept in the Natural History Museum in London , England (Catalog No. 1984,843 and E.1036) and in the National Museum of Natural History in Washington, DC , USA (Catalog No. 163039).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the laphamite belonged to the mineral class of "sulphides and sulphosalts" and there to the department of "sulphides with non-metallic character", where together with alacranite , auripigment , dimorphine , duranusite , Jeromit (discredited 2006), Realgar , Pararealgar and Uzonit formed the unnamed group II / F.02 .

In contrast , the 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies laphamite in the “Sulphides of Arsenic, Alkalis; Sulphides with halides, oxides, hydroxides, H 2 O “. This is further subdivided according to the predominant anions in the compound , so that the mineral can be found according to its composition in the sub-section "with As, (Sb), S", where it is only together with auripigment the "auripigment group" with the System no. 2.FA.30 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns laphamite to the class of "sulfides and sulfosalts" and there to the department of "sulfide minerals". Here he is the only member of the unnamed group 11/02/06 within the subsection “Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 2: 3”.

Crystal structure

Laphamite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a  = 11.86  Å ; b  = 9.76 Å; c  = 4.27 Å and β = 90.2 ° and two formula units per unit cell . Template: room group / 14.2

Education and Locations

Laphamite is formed as a secondary mineral (probably through sublimation ) and forms encrustation on the surface of cinder blocks in burning anthracite coal heaps. Arsenolite and auripigment appear as accompanying minerals .

The mineral is so rare that so far (as of 2015) it could only be detected at its type locality Burnside (Northumberland County, Pennsylvania).

See also

literature

  • Pete J. Dunn, Donald R. Peacor, Alan J. Criddle, Robert B. Finkelman: Laphamite, an Arsenic Selenide Analogue of orpiment, from Burning Anthracite Deposits in Pennsylvania. In: Mineralogical Magazine. Volume 50, 1986, pp. 279–282 ( PDF 1.1 MB )

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC # page = 98 List of Mineral Names; March 2015 (PDF 1.5 MB)
  2. ^ A b c 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.  112 .
  3. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  4. ↑ a b c d Laphamite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 61.7 kB )
  5. ↑ List of localities for laphamite in the Mineralienatlas and Mindat