Hemimorphite
| Hemimorphite | |
|---|---|
 (size 14.4 cm × 6.5 cm × 3.9 cm) |
|
| General and classification | |
| other names |
Fumed silica |
| chemical formula | Zn 4 [4] [(OH) 2 | Si 2 O 7 ] • H 2 O |
|
Mineral class (and possibly department) |
Silicates and Germanates - group silicates |
|
System no. to Strunz and to Dana |
9.BD.10 ( 8th edition : VIII / C.07) 56.01.02.01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal; mm 2 |
| Space group | Imm 2 (No. 44) |
| Lattice parameters | a = 8.37 Å ; b = 10.73 Å; c = 5.12 Å |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 4.5 to 5 |
| Density (g / cm 3 ) | measured: 3.475; calculated: 3.484 |
| Cleavage | completely after {110}, indistinct after {101}, rarely after {001} |
| Break ; Tenacity | uneven |
| colour | colorless, white, light blue, light green, gray, brown |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass luster to diamond luster; mother-of-pearl on cleavage surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.614 n β = 1.617 n γ = 1.636 |
| Birefringence | δ = 0.022 |
| Optical character | biaxial positive |
| Axis angle | 2V = 46 ° (measured); 44 ° (calculated) |
Hemimorphite , outdated also known as silica zinc , is a frequently occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the orthorhombic crystal system with the composition Zn 4 [4] [(OH) 2 | Si 2 O 7 ] · H 2 O, so chemically speaking it is a water-containing zinc silicate with additional hydroxide ions that structurally belongs to the group silicates .
Hemimorphite mainly develops tabular crystals up to 10 centimeters in length, which are streaked along the c-axis and have a glass-like to diamond-like sheen . However, sheaf-shaped and radial-rayed and grape-like, granular or coarse mineral aggregates are also known .
In its pure form it 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 blue, light green, gray or brown color, the transparency decreasing accordingly. However, the line color is always white.
Etymology and history
(size of the crystals approx. 1 mm)
The word Hemimorphite is a composition of the ancient Greek words ἡμι- hemi for "half" (derived from ἥμισυς hémisys [ ʰɛ̌ːmisys ] "half and half") and μορφή morphé [ morpʰɛ̌ ] for "shape", composed so "half figure". The term refers to the hemimorphic (half-shaped) crystal forms that are often found in nature , which have different crystal faces at one end than at the other. This term was coined in 1853 by Gustav Adolf Kenngott .
However, under the mining name of silica zinc , the mineral had been known by J. F. August Breithaupt at least since 1823 and previously also under the misleading name of calamine . To distinguish it from Noble Galmei Smithsonite , James LM Smithson introduced the name Kieselgalmei in 1802 .
The type locality is the Băița mining district (Hungarian: Rézbánya ) in the Bihor district in Romania.
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the hemimorphite belonged to the department of " group silicates (sorosilicates)", where together with Bertrandite and Junitoite it formed the unnamed group VIII / C.07 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies hemimorphite in the category of “group silicates”. This is, however, now further subdivided according to the type of silicate building groups, the possible presence of further anions and the coordination of the cations , so that the mineral is classified in the sub-section “Si 2 O 7 groups with additional anions; according to its composition and structure ; Cations in tetrahedral [4] and / or other coordination ”can be found, where it is the only member of the unnamed group 9.BD.10 .
In the systematics of minerals according to Dana , which is mainly used in the English-speaking world, the departments are already divided according to the type of group formation and possible additional anions. Here the hemimorphite is accordingly the only member in the unnamed group 56.01.02 within the subdivision “ Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] coordination ”.
Crystal structure
Hemimorphite crystallizes orthorhombically in the space group Imm 2 (space group no. 44) with the lattice parameters a = 8.37 Å ; b = 10.73 Å and c = 5.12 Å as well as 2 formula units per unit cell .
The crystal structure consists of double tetrahedra [Si 2 O 7 ] 6− , which are linked to one another via common corners, and Zn 2 O 6 OH double tetrahedra, which are linked via a shared hydroxide ion (OH) - . The water of crystallization H 2 O is stored in the larger cavities formed by the tetrahedra .
properties
When hemimorphite is heated up to 550 ° C, half of the water of crystallization escapes evenly, which means that the crystals become cloudy, but the crystal structure is retained. The crystal lattice only disintegrates when the constitution water, i.e. the hydroxide ions, also escape when heated to 650 ° C.
Hemimorphite is pyroelectric , so it builds up an electric charge when the temperature changes periodically.
Education and Locations
.jpg)
Hemimorphite forms mainly secondary in the oxidation zones of galena - sphalerite displacement deposits . As Begleitminerale next galena and sphalerite occur, you still Anglesite , Aurichalcit , calcite , Cerussite , chrysocolla , Hydrozinkit , Rosasit and Smithsonite .
Hemimorphite has so far (as of 2012) been detected at over 1400 sites worldwide. In addition to its type locality Băița, the mineral occurred in Romania at Dolea in Bihor County and at Dognecea and Ocna de Fier in Caraș-Severin County .
In Germany hemimorphite was found in many places in the Black Forest and Odenwald in Baden-Württemberg; in several places in Lower and Upper Bavaria ; in many places in the Harz region of Lower Saxony ; near Stolberg , in the Eifel , in the Niederbergischen and Sauerland in North Rhine-Westphalia; in some places in Rhineland-Palatinate and Saxony-Anhalt ; in the Saxon Ore Mountains and Vogtland as well as near Gräfenroda in Thuringia.
In Austria, the mineral was found mainly in Carinthia (Bleiberg, Gurktal Alps, Hohe Tauern, Karawanken), Lower Austria , Salzburg (Hohe Tauern), Styria (Fischbacher Alps), North Tyrol and Vorarlberg .
In Switzerland, hemimorphite has so far been found mainly in the cantons of Graubünden and Valais , but has also occurred in Seltisberg (Basel-Land), Malcantone (Ticino) and Bex (Vaud).
The largest known crystals of up to 10 centimeters in length were discovered in Bisbee (Arizona) .
Other locations are found in Egypt, Algeria, Angola, Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, the Democratic Republic of the Congo and the neighboring Republic of the Congo, Finland, France, Greece, Greenland, Guatemala, India, Iran, Ireland, Italy, Japan, Yemen, Canada, Kazakhstan, Korea, Morocco, Mexico, Namibia, New Caledonia, Norway, Peru, Poland, Portugal, Russia, Zambia, Sweden, Zimbabwe, Slovakia, Slovenia, Spain, South Africa , Tajikistan, Thailand, Tunisia, the Czech Republic, Hungary, the United Kingdom (Great Britain), the United States of America (USA) and Vietnam.
use
Hemimorphite is used as zinc ore when it is locally accumulated.
See also
literature
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 690–691 (first edition: 1891).
Web links
- Mineral Atlas: Hemimorphite (Wiki)
Individual evidence
- ↑ a b c d e 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. 573 .
- ↑ Webmineral - Hemimorphites .
- ↑ a b c Hemimorphites . 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; 73 kB ; accessed on January 18, 2018]).
- ↑ a b c d e f Mindat - Hemimorphite (English).
- ^ Adolf Kenngott: Hemimorphite . In: The Mohs' mineral system . Carl Gerold & Sohn, Vienna 1853, p. 67–68 (1853_Kenngott_Das_Mohssche_Mineralsystem_67.pdf [PDF; 120 kB ; accessed on January 18, 2018]).
- ^ A b c d Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 718-719 .
- ↑ Mindat - type locality: Băiţa Mining District (Baita Bihor; Rézbánya), Nucet, Bihor Co., Romania
- ↑ 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. 498-500 .
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (= Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 212 .
- ↑ Find location list for hemimorphite at the Mineralienatlas and at Mindat .