Gibbsite
| Gibbsite | |
|---|---|
 |
|
| General and classification | |
| other names |
Hydragillite or hydrargillite |
| chemical formula | γ-Al (OH) 3 |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.FE.10 ( 8th edition : IV / F.02) 06.03.01.01 |
| Similar minerals | Chalcedony , hemimorphite , smithsonite , wavellite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 1 / n (No. 14, position 2) |
| Lattice parameters |
a = 8.66 Å ; b = 5.07 Å; c = 9.72 Å β = 94.5 ° |
| Formula units | Z = 8 |
| Frequent crystal faces | {001}, {101}, {110} |
| Twinning | very often after [130] parallel to {001}, often {001}, less often after {100} and {110} |
| Physical Properties | |
| Mohs hardness | 2.5 to 3.5 |
| Density (g / cm 3 ) | measured: 2.40; calculated: [2.42] |
| Cleavage | completely after [001] |
| Break ; Tenacity | uneven |
| colour | colorless, white, gray, green, blue |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss, mother-of-pearl, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.568 to 1.570 n β = 1.568 to 1.570 n γ = 1.586 to 1.587 |
| Birefringence | δ = 0.018 |
| Optical character | biaxial positive |
Gibbsite , also known under the synonym hydragillite or hydrargillite , is a rather seldom occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the chemical composition γ-Al (OH) 3 , so it is an aluminum hydroxide .
Gibbsite develops only small, tabular or twinned pseudo-hexagonal crystals up to about three centimeters in size. It is usually found in the form of leafy, scaly, grape or earthy mineral aggregates and crusty coatings. Undamaged crystal surfaces have a glass-like sheen , whereas the fissure surfaces have a more mother-of-pearl shimmer and crusty, earthy aggregates are matt. In its pure form, gibbsite 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 gray, greenish or bluish color, the transparency decreasing accordingly.
With a Mohs hardness of 2.5 to 3.5, gibbsite is one of the soft to medium-hard minerals that, like the reference mineral calcite (3), can be easily scratched with a copper coin or like fluorite (4) with a pocket knife.
Because of its similarity in shape and color, gibbsite can be confused with chalcedony , hemimorphite , smithsonite, and wavellite . However, all of the minerals mentioned are harder than gibbsite.
Etymology and history
.jpg)
Gibbsite was first discovered near Richmond in Berkshire County , Massachusetts and described in 1822 by John Torrey , who named the mineral after General George Gibbs (1776–1833), a US mineral collector whose mineral collection was from Yale in the 19th century University was bought up.
The synonym Hydra (r) gillit is a combination of the ancient Greek words ὕδωρ [hydōr] for water and ἄργιλλος [árgillos] for white clay or earthenware .
classification
Already in the now outdated, but still common 8th edition of the mineral classification according to Strunz , the gibbsite belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates (water-containing oxides with a layered structure)", where it together with bayerite , Doyleit and Nordstrandit formed the unnamed group IV / F.02 .
The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the International Mineralogical Association (IMA), also assigns the gibbsite to the class of "oxides and hydroxides", but in the department of "hydroxides (without V or U ) " a. This is further subdivided according to the possible presence of hydroxide ions and / or crystal water as well as the crystal structure, so that the mineral is classified according to its composition and structure in the subdivision of “hydroxides with OH, without H 2 O; Layers of edge-linked octahedra "can be found where the" Gibbsite group "with the system no. 4.FE.10 and the other members Bayerit, Doyleit and Nordstrandit.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the gibbsite to the class of "oxides and hydroxides" and there in the department of "hydroxides and hydroxide-containing oxides". Here he is to be found as the only member of the unnamed group 06.03.01 within the subdivision of " Hydroxides and hydroxy-containing oxides with (OH) 3 - or (OH) 6 groups ".
Crystal structure
Gibbsite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a = 8.66 Å ; b = 5.07 Å; c = 9.72 Å and β = 94.5 ° and 8 formula units per unit cell .
The crystal structure of gibbsite consists of hydroxide double layers parallel (100). According to [001], Al 3+ ions are embedded in the octahedral gaps in these layers . Only weak Coulomb and Van der Waals forces act between the double layers , which is the reason for the easy cleavage according to [001].
properties
When heated to over 100 ° C, gibbsite loses part of its water of crystallization and turns into diaspore (α-AlO (OH)). Further heating to about 300 ° C drives out the remaining crystal water.
Modifications and varieties
Gibbsite is one of three modifications of aluminum hydroxide . The other two are bayerite and north strandite .
Education and Locations
Gibbsite is a secondary mineral that is formed as a conversion product either through oxidation or metamorphosis in hydrothermal veins of aluminum-rich rocks . Together with boehmite , diaspore , hematite , goethite , kaolinite and small proportions of rutile and anatase , gibbsite forms the rocks bauxite and laterite .
As a rather rare mineral formation, gibbsite can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2013) around 400 sites are known to be known. In addition to its type locality Richmond , the mineral occurred in Massachusetts among others in the Stockbridge Valley and Lenox in Berkshire County . Furthermore, the it was in the United States of America still many places in Alabama and Georgia as well as in some places in Arizona , Arkansas , Colorado , Indiana , California , Mississippi , Nevada , New Mexico , North Carolina , Oregon , Utah and Virginia found .
Slatoust in the Urals in Russia, where tabular crystals up to 10 cm in size were discovered, is known for its extraordinary gibbsite finds .
In Germany, gibbsite is known from the “Haus Württemberg” mine near Freudenstadt and the “Michelsberg” quarry at Katzenbuckel in Baden-Württemberg; from the wheel of fortune mine near Oberschulenberg in Lower Saxony; the copper mines near Marsberg and the mining association Eisenzecher Zug near Eiserfeld in North Rhine-Westphalia; at the Schellkopf near Brenk , near Bad Ems and in the Friedrichssegen mine near Frücht in Rhineland-Palatinate as well as in the Bärenstein quarry and the “Deutschlandschacht” mine near Oelsnitz / Erzgeb. in Saxony.
In Austria the mineral was found in a graphite quarry near Amstall and Trandorf in Lower Austria; on the Grieswies-Schwarzkogel in the Goldberg Group , near Weitwörth ( Oberndorf near Salzburg ) and on the Untersberg in Salzburg; on the Brandberg near Leoben in Styria and near Zirl in Tyrol.
Other locations include Egypt, Albania, Argentina, Australia, Belgium, Bolivia, Brazil, China, the Democratic Republic of the Congo (Zaire), the Dominican Republic, Ecuador, France, Greece, Greenland, Guinea, Guyana, India, Indonesia, Iran, Iraq, Ireland, Israel, Italy, Jamaica, Japan, Cambodia, Cameroon, Canada, Kazakhstan, Colombia, Cuba, Luxembourg, Madagascar, Malaysia, Mauritania, Namibia, the Netherlands, New Zealand, Nigeria, Norway, Peru, Poland, Romania , Sweden, Serbia, the Seychelles, Slovakia, Spain, South Africa, Sudan, Suriname, Czech Republic, Hungary, the United Kingdom (England, Wales).
use
The composite material Corian (brand name of Dupont) consists of about 66% of its weight of very fine-grained gibbsite as a filler and about 33% of polymethyl methacrylate (PMMA), which forms the matrix. Corian is used to design non-porous, seamless surfaces in kitchens, laboratories and hospitals, especially for work surfaces.
See also
literature
- Gibbsite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 70 kB )
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 549 (first edition: 1891).
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 480-483 .
- 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. 420-421 .
Web links
- Mineral Atlas: Gibbsite (Wiki)
- Webmineral - Gibbsite (English)
Individual evidence
- ^ A b c 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. 238 .
- ↑ a b c Gibbsite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 70 kB )
- ↑ a b Mindat - Gibbsite (English)
- ↑ a b Martin Okrusch, Siegfried Matthes: Mineralogy: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 , pp. 58 .
- ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
- ↑ Mineralogical Record: George Gibbs (1776-1833)
- ^ Rudolf Köster: Proper names in the German vocabulary . de Gruyter, Berlin [a. a.] 2003, ISBN 978-3-11-017702-2 , pp. 56 ( limited preview in Google Book search).
- ^ Wilhelm Pape : Concise dictionary of the Greek language. Braunschweig 1914, Volume 1, p. 345 ( ἄργιλλος ) and Volume 2, p. 1175 ( ὕδωρ )
- ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 481 .
- ↑ Mindat - Number of localities for Gibbsite
- ^ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 109 .
- ↑ Find location list for Vicanit- (Ce) in the Mineralienatlas and in Mindat