Helvin

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Helvin
Helvite-186660.jpg
Helvin (yellow) with muscovite (gray) on feldspar (white) from the "Wushan Spessartine Mine", Tongbei, Yunxiao , Fujian Province, China
(size: 3.5 × 3.1 × 1.3 cm)
General and classification
chemical formula Mn 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)
76.02.04.01
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  = 8.29  Å
Formula units Z  = 2
Frequent crystal faces {111}, {1 1 1}, occasionally also {211}, {110}, {100}
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 3.20 to 3.44; calculated: [3.23]
Cleavage imperfect after (101)
Break ; Tenacity uneven to scalloped
colour gray-yellow to green-yellow, red, brown
Line color White
transparency transparent to translucent
shine greasy glass gloss
Crystal optics
Refractive index n  = 1.728 to 1.749
Birefringence none, as isotropic

Helvin is a rather seldom occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the cubic crystal system with the chemical composition Mn 4 [S | (BeSiO 4 ) 3 ], so chemically speaking it is a manganese - sulfur - beryllium silicate. Structurally it belongs to the framework silicates .

Helvin is the eponymous mineral of the "Helvin series" and, as a manganese analogue, forms a continuous mixed crystal series with the ferrous end member danalite (Fe 4 [S | (BeSiO 4 ) 3 ]) and the zinc-containing end member Genthelvin (Zn 4 [S | (BeSiO 4 ) 3 ]).

The mineral is transparent to translucent and mostly develops isometric, tetrahedral and dodecahedral or pseudo- octahedral crystals , but is also found in the form of granular or spherulitic mineral aggregates . Its color usually varies between a light gray-yellow to greenish-yellow. Due to its mixed crystal formation with Danalith and Helvin as well as various foreign admixtures , it can also take on a red to brown color. The crystal surfaces have a greasy glass luster .

With a Mohs hardness of 6 to 6.5, Helvin is still one of the medium-hard minerals that, like the reference mineral orthoclase (6), can be scratched with a steel file.

Etymology and history

Light yellow Helvin from the type locality Breitenbrunn in the Ore Mountains (field of view 1.5 cm)

The name Helvin, which is still valid today, was given to the mineral in 1817 by Abraham Gottlob Werner , who named it after the Greek word ἥλιος (helios) for sun due to its predominantly yellow color .

However, Helvin was known and described even before Werner's notes, among others by Friedrich Mohs (as an appendix to the Granat in the mineral cabinet of the Viennese banker Van der Nüll described in 1829; Section I, pp. 92-93) and by Johann Carl Freiesleben in his “Geognostischen Contributions ”(Volume 5, p. 126 f.).

The "Brothers Lorenz" and "Friedefürst" mines near Breitenbrunn / Erzgeb are considered type localities. in the Saxon Erzgebirgskreis .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Helvin belonged to the department of " framework silicates (tectosilicates), with zeolites ", where he named the "Helvin series" with the system no. VIII / J.12 and the other members Danalith and Genthelvin .

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 Helvin in the department of “tectosilicates without zeolitic H 2 O”. This 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 , Genthelvin, 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 Helvin to the class of "silicates and Germanates" and there in the department of "framework silicates: Al-Si lattice". Here he is together with Genthelvin 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

Helvin crystallizes cubically in the space group P 4 3 n (space group no. 218) with the lattice parameter a  = 8.29  Å and 2 formula units per unit cell . Template: room group / 218

properties

When heated, Helvin puffs up and melts into a yellowish-brown, opaque glass . The mineral is soluble in hydrochloric acid , releasing hydrogen sulfide .

Education and Locations

Helvin (yellow) on rhodonite (pink) from Pachapaqui, Bolognesi Province , Peru (field of view 8 mm)
Almost black Helvin with golden-yellow Spessartine on white orthoclase from the "Wushan Spessartine Mine", Tongbei, Yunxiao , Fujian, China
(size: 5.1 × 4.0 × 2.3 cm)
Yellow Helvin enclosed in quartz from the "Yaogangxian Mine", Yizhang , Hunan, China (size: 6.7 × 4.2 × 3.7 cm)

Helvin forms in igneous rocks such as granite pegmatites and alkaline syenites , but can also occur hydrothermally in old men and skarns and through metasomatosis (material displacement) in deposits . The accompanying minerals include albite , amazonite , augite , various chlorites and garnets , columbite , diopside , fluorite , magnetite , phenakite , rhodonite , sphalerite , vesuvianite , willemite and wolframite .

As a rather rare mineral formation, Helvin can sometimes be abundant at different sites, but overall it is not very common. Around 230 sites are known to date. Besides its type locality, the pits "brothers Lorenz" and " Prince of Peace " in Breitenbrunn mineral "occurred in Germany or in other mines in Saxony such as, but luck unexpectedly at the Eighth " in Antonsthal and "Yellow Birch" in Beierfeld and in Johanngeorgenstadt and Königshain . In addition, Helvin could still be found in some quarries in the area of Tittling in Bavaria and in the Henneberg quarry near Weitisberga in Thuringia.

The "Sawtooth Batholithe " in the Sawtooth Mountains (Sawtooth Range) in Boise County of the US state Idaho, where cubic Helvin crystals with a diameter of up to 2.5 centimeters were discovered, are known for their extraordinary Helvin finds . However, crystals up to 12 centimeters in size are said to have been found at other sites.

In Austria, Helvin is only known from the Doppelbachgraben (Tobelbachgraben) near Maiersch in Lower Austria, from the Friedlkogel and Kaskogel on the Kaiblinggraben near Kleinveitsch in Styria and from the Oberschrammach glacier on the Schrammacher in the Tyrolean Zillertal.

In Switzerland, the mineral has so far only been found on Forno and Pizzi dei Rossi in Val Forno , a side valley of Val Bregaglia ( Bergell ) in the canton of Graubünden.

Other locations include Argentina, Australia, Brazil, Bulgaria, China, France, Greenland, Italy, Japan, Canada, Kazakhstan, Kyrgyzstan, Malawi, Mexico, Namibia, Norway, Pakistan, Peru, Poland, Portugal, Romania, Russia, Sweden, Spain, South Africa, the Czech Republic, the United Kingdom (England) and the United States of America (Alaska, Arizona, Arkansas, Colorado, Idaho, California, Montana, Nevada, New Hampshire, New Mexico, North Carolina, Texas, Utah, Virginia, Wisconsin).

use

Helvin is normally of no importance as a raw material, but if it is locally accumulated it can be valuable as beryllium ore.

See also

literature

Web links

Commons : Helvine  - 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 . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  699 .
  2. ↑ Webmineral: Helvite
  3. ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 902-903 .
  4. ↑ a b Helvite ( Helvine ), In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 65.6 kB )
  5. ↑ Mindat: Helvine
  6. ^ Austrian State Museum - The mineral collection of the Counts Thurn-Valsassina at Bleiburg Castle. Part 1: On the history of an old collection by Heinz Meixner (PDF 11.9 MB; p. 6)
  7. ^ AG Werner : Helvin , In: Craz, Gerlach, Carl Gerold (Ed.): Last Mineral System , Freiberg and Vienna 1817, p. 29 ( PDF 101.1 kB )
  8. ↑ a b 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.  545 .
  9. ↑ Mindat: Number of locations for Helvine
  10. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 270 ( Dörfler Natur ).
  11. ↑ Find location list for Helvin in the Mineralienatlas and Mindat