Genthelvin

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Genthelvin
Genthelvite-503826.jpg
Huanggang Fe-Sn Deposit (Huanggangliang Mine), Hexuchten-Banner , Inner Mongolia Autonomous Region, China
(size: 18 × 18 × 14 mm)
General and classification
chemical formula Zn 4 [S | (BeSiO 4 ) 3 ]
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates (tectosilicates)
System no. to Strunz
and to Dana 		9.FB.10 ( 8th edition : VIII / J.12)
76.02.04.03
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic-hexakistrahedral; 4  3  m
Space group P 4 3 n (No. 218)Template: room group / 218
Lattice parameters a  = 8.15  Å
Formula units Z  = 2
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 3.44 to 3.70; calculated: 3.70
Cleavage indistinct after {111}, {1 1 1}
Break ; Tenacity uneven; brittle
colour colorless, light to emerald green, pink to red, yellow to yellow-brown
Line color White
transparency transparent
shine Glass luster; Greasy to resinous sheen on broken surfaces
Other properties
Special features occasionally green fluorescence and phosphorescence

Genthelvin is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the cubic crystal system with the chemical composition Zn 4 [S | (BeSiO 4 ) 3 ]

Genthelvin is the zinc analogue of the iron-containing danalite (Fe 4 [S | (BeSiO 4 ) 3 ]) and manganese-containing helvin (Mn 4 [S | (BeSiO 4 ) 3 ]) and forms with each of them a continuous row of mixed crystals .

In its pure form, Genthelvin is colorless and transparent. Since it forms mixed crystals with Danalith and Helvin on the one hand and on the other hand can contain various foreign admixtures , it usually occurs in different colors, with light to emerald green, pink to red and yellow to yellow-brown colors predominating. However, Genthelvin always leaves a white line on the notice board .

The mineral usually develops tetrahedral or tristrahedral crystals , but is also found in the form of irregular segregations. Undamaged crystal surfaces have a glass-like gloss , whereas fracture surfaces have a greasy to resinous gloss .

Etymology and history

Genthelvin was named on the one hand because of his close relationship with Helvin and on the other hand in honor of the German-American chemist and mineralogist Friedrich August Genth , who first described the mineral in 1892 without giving it a name.

Genthelvin was first discovered at St. Peters Dome (West Cheyenne Canon), an extension of Pikes Peak about 10 kilometers southwest of Colorado Springs in El Paso County of the US state of Colorado and described in 1944 by Jewell J. Glass, Richard H. Jahns and Rollin E. Stevens.

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Genthelvin belonged to the department of the " framework silicates (tectosilicates), with zeolites ", where he together with danalite and Helvin the "Helvin series" with the system no. VIII / J.12 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), classifies the Genthelvin under the category of “tectosilicates without zeolitic H 2 O”. This section is further subdivided according to the possible presence of additional anions , so that the mineral can be found according to its composition in the sub-section “Tectosilicates with additional anions”, where it can be found together with Bicchulite , Danalith, Haüyn , Helvin, Kamaishilith , Lasurit , Nosean , Sodalith , Tsaregorodtsevit and Tugtupit the "Sodalite-Danalith Group" with the system no. 9.FB.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Genthelvin to the class of "silicates and Germanates" and there in the department of "framework silicates: Al-Si lattice". Here he is together with Helvin and Danalith in the " Helvingruppe " with the system no. 76.02.04 within the sub-section "Framework silicates: Al-Si lattices, feldspar representatives and related species".

Crystal structure

Genthelvin crystallizes cubically in the space group P 4 3 n (space group no. 218) with the lattice parameter a  = 8.15  Å and 2 formula units per unit cell . Template: room group / 218

properties

Genthelvin forms an unclear pearl in front of the soldering tube . The mineral decomposes in strong hydrochloric acid , producing hydrogen sulfide with its characteristic odor of rotten eggs.

Under UV light , some genthelvins show green fluorescence with subsequent phosphorescence .

Education and Locations

Genthelvin (yellow) on aegirine (black) and albite (white) from the Poudrette quarry, Mont Saint-Hilaire , Canada (size of the genthelvin measured over the edge ≈ 8–9 mm)
Grass-green Genthelvin from the same site (size: 2 cm × 1.3 cm × 1.2 cm)

Genthelvin forms in miarolitic cavities of granitic or alkaline pegmatites and syenites , as well as in old men and skarns . As Begleitminerale occur among other Bertrandit , Gahnit , Hambergit , microcline , Phenakit , quartz , siderite , sphalerite , topaz , Willemit , various zeolites and / or zirconium on.

As a rare mineral formation, Genthelvin could only be proven at a few sites, with around 60 sites being known to date. In addition to its type locality St. Peters Dome (West Cheyenne Canon), the mineral occurred at other locations in Colorado such as Stove Mountain (Cookstove Mountain) in El Paso County and in Crystal Peak in Teller County . Other previously known sites in the United States of America (USA) are Rockport in Essex County (Massachusetts) ; Blue Mountyin , Iron Mountain, and Sugarloaf Mountain in New Hampshire ; several sites in the mining area around Franklin (New Jersey) and Cumberland (Rhode Island) as well as the Washington Pass in Okanogan County (Washington).

Other locations include Argentina, Brazil, China, Greenland, Italy, Japan, Canada, Kazakhstan, Malawi, Mongolia, Niger, Nigeria, Norway, Pakistan, Romania, Russia, Zambia, Ukraine and the United Kingdom ( England , Scotland ).

use

Despite its relatively high zinc content of around 40%, Genthelvin has so far been of no economic importance due to its rarity. However, since it sometimes forms beautifully colored and transparent crystals, it is occasionally offered to collectors in various gemstone cuts.

See also

literature

  • JJ Glass, RH Jahns, RE Stevens: Helvite and danalite from New Mexico and the helvite group , In: American Mineralogist , Volume 29 (1944), pp. 163–191 ( PDF 1.5 MB )

Web links

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

Individual evidence

  1. ↑ a b c d e f g 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.  699 .
  2. ↑ a b Webmineral - Genthelvite
  3. ↑ a b Genthelvite . 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; 71  kB ]).
  4. ^ JJ Glass, RH Jahns, RE Stevens: Helvite and danalite from New Mexico and the helvite group . In: 'American Mineralogist . tape 29 , 1944, pp. 164 ( rruff.info [PDF; 1.5 MB ; accessed on April 13, 2018]).
  5. ↑ a b Mindat - Genthelvite
  6. ^ Mineralienatlas - type locality St. Peters Dome
  7. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  786–787 (first edition: 1891).
  8. ↑ Mindat - Number of locations for Genthelvin
  9. ↑ location list for the Genthelvin Mineralienatlas and Mindat
  10. ↑ realgems.org - Genthelvit (with examples of polished genthelvine)