Gibbsite
- Hydragillit or gibbsite
Gibbsite, also known under the synonym Hydragillit or gibbsite, is a rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the chemical composition of γ -Al (OH) 3, and is therefore an aluminum hydroxide.
Gibbsite developed only small, tabular or pseudo-hexagonal crystals by twinning to about three inches size. He usually finds himself bladed, flaky, racemose or earthy mineral aggregates and crusty coatings in the form. Uninjured crystal surfaces have a glass-like luster, cleavage surfaces shimmer on the other hand rather nacreous and crusty, earthy aggregates are dull. In its pure form gibbsite is colorless and transparent. But it may also appear white and accept by foreign admixtures a gray, greenish or bluish color through multiple light refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly.
With a Mohs hardness of 2.5 to 3.5 gibbsite heard can scratch with a penknife to the soft to medium-hard minerals that are similar as the reference mineral calcite ( 3) with a copper coin or as fluorite ( 4) easily.
Due to its similarity in shape and color gibbsite with chalcedony, hemimorphite, smithsonite and Wavellite can be confused. However, all of these minerals are harder than gibbsite.
Special Features
When heated to about 100 ° C gibbsite loses part of its water of crystallization and changes in diaspore ( α - AlO ( OH) ) to. Further heating to about 300 ° C, drives off the remaining water of crystallization.
Etymology and history
Was first discovered gibbsite in Richmond, Berkshire County of the U.S. state of Massachusetts and described in 1822 by John Torrey, of the minerals by General George Gibbs ( 1776-1833 ) named, a US-based mineral collector, whose collection of minerals in the 19th century by the Yale was bought University.
The synonym Hydra (r) is gillit a composition from the ancient Greek words ὕδωρ [ Hydor ] for water and ἄργιλλος [ árgillos ] for white clay or pottery earth.
Classification
Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of gibbsite to mineral class of " oxides and hydroxides " and then to the Department of " hydroxides and oxide hydrates ( hydrous oxides with layered structure ) ," where he along with bayerite, Doyleit and nordstrandite the unnamed group IV/F.02 formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the gibbsite also in the class of " oxides and hydroxides ," there but in the department of the " Hydroxide (without V or U) " a. This is also further divided by the possible presence of hydroxide ions and / or crystal water, as well as the crystal structure, so that the mineral according to its composition, and its structure in the sub-division of the " hydroxides with OH, excluding H2O; Layers of edge-sharing octahedra " is to find where it is named as the " Gibbsitgruppe "with the system no. Forms 4.FE.10 and the other members bayerite, Doyleit and nordstrandite.
The mainly common in English-speaking classification of minerals according to Dana assigns the gibbsite in the class of " oxides and hydroxides " and there in the department of " hydroxides and hydroxy- oxides " one. Here he is the only member of the unnamed group 06:03:01 within the sub-division of - to find " hydroxides and hydroxy- oxides (OH ) 3 or (OH ) 6 groups ".
Modifications and varieties
Gibbsite is a modification of the three of the aluminum hydroxide. The other two are bayerite and nordstrandite.
Education and Locations
Gibbsite is a secondary mineral that forms as a conversion product either by oxidation or metamorphosis in hydrothermal veins aluminum-rich rocks. Together with boehmite, diaspore, hematite, goethite, kaolinite, and small amounts of rutile and anatase forms gibbsite bauxite and laterite, the rocks.
As a rather rare mineral gibbsite formation can indeed be abundant in part to different sites, overall it is not very common. So far (as of 2013) are considered to be known around 400 localities. Apart from its type locality Richmond mineral occurred in Massachusetts among other things still in Stockbridge Valley and Lenox in Berkshire County. Furthermore, it could be found in the United States of America nor in 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.
Known due to exceptional Gibbsitfunde among other Zlatoust in the Ural Mountains in Russia, where up to 10 cm large, tabular crystals were discovered.
In Germany you know gibbsite far from the pit " house Württemberg" in Freudenstadt and the quarry " Michel Berg" on Katzenbuckel in Baden- Württemberg; from the pit wheel of fortune at Oberschulenberg in Lower Saxony; the copper mines at Mars Hill and pit composite Eisenzecher train at Eiserfeld in North Rhine-Westphalia; on the clamp head at Brenk, near Bad Ems and in the pit Friedrichssegen at Frücht in Rhineland -Palatinate and in the quarry stone and bears the Pit " Germany Shaft" in Oelsnitz / Erzgeb. in Saxony.
In Austria, found the mineral, among others, in a graphite quarry near Amstall and Trandorf in Lower Austria; am Gries Wies- Schwarzkogel the Goldberg group at Weitwörth ( Oberndorf bei Salzburg) and on the lower mountain in Salzburg; the Brandberg in Leoben in Styria and in Zirl in Tyrol.
Other localities lie among others in Albania, Argentina, Australia, Belgium, Bolivia, Brazil, China, the Democratic Republic of 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, Seychelles, Slovakia, Spain, South Africa, Sudan, Suriname, Czech Republic, Hungary, the United Kingdom (England, Wales).
Crystal structure
Gibbsite crystallized in the monoclinic space group P21 / n ( Raumgruppen-Nr. 14) with the lattice parameters a = 8.66 Å; b = 5.07 Å; c = 9.72 Å and 94.5 ° β = and 8 formula units per unit cell.
The crystal structure of gibbsite is from hydroxide bilayers in parallel ( 100). In the octahedral interstices of these layers ions are incorporated by Al3. Between the bilayers only weak Coulomb and van der Waals forces, which is the cause of the slight cleavage after work.
Use
The composite material is made of Corian to about 66 % of its weight of gibbsite and about 33% of polymethylmethacrylate (PMMA ); it is used for the design of non-porous, seamless surfaces in kitchens, laboratories and hospitals.