Hemimorphite
( Size: 14.4 x 6.5 x 3.9 cm)
- Kieselzinkerz
Hemimorphite outdated, also referred to as Kieselzinkerz, is a commonly occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the orthorhombic crystal system with the composition Zn4 [( OH) 2 | Si2O7 ] · H2O, that is chemically a hydrous zinc silicate with additional hydroxide ions that structurally belongs to the group of silicates.
Hemimorphite mainly developed tabular crystals up to 10 centimeters in length, which are striped by the c-axis and have a glass - to diamond-like luster. But are also known sheaf -shaped and radial- and grape-like, granular, or coarse mineral aggregates.
In its pure form it is colorless and transparent. But it may also appear white and accept by foreign admixtures, a light blue, light green, gray or brown color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. However, the stroke color is always white.
Special Features
Upon heating of hemimorphite up to 550 ° C, the half of the crystal water escapes evenly, thereby Although the crystals are turbid, the crystal structure, however, is still maintained. Only when the water of constitution, that is, escapes the hydroxide by heating to 650 ° C, breaks up the crystal lattice.
Hemimorphite is pyroelectric, that builds on periodic change in the temperature, an electric charge.
Etymology and history
The word hemimorphite is a composition of the ancient Greek words ἡμι HEMI for half (originally ἥμισυς [ ʰ ɛ̌ ː Misys ] for half or τὸ ἥμισυ half) and μορφή [ morp ʰ ɛ̌ ] morphé for shape, that is composed half shape. The term takes with respect to the in nature often vorzufindenden hemimorphic (half multiform ) crystal form which at one end has other facets than the other. Was coined this term in 1853 by Gustav Adolf Kenngott.
Under the name Kieselzinkerz mining the mineral already at least since 1823, however, was by JF August Breithaupt known and previously under the misleading name calamine. To distinguish the Noble calamine Smithsonite James LM Smithson led, however, in 1802 the name Kieselgalmei one.
As a type locality applies the mining district Baita (Hungarian: Rézbánya ) in Bihor County in Romania.
Classification
Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of hemimorphite to the Department of " group silicates ( Sorosilikate ) " where he was the unnamed group VIII/C.07 together with Bertrandit and Junitoit.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Hemimorphite also in the department of " group silicates " one. This is, however, now further divided by type of silicate boards, the possible presence of other anions and the coordination of the cations, so that the mineral according to its composition, and its build-up in the subsection " Si2O7 groups with additional anions; Cations can be found in tetrahedral and / or other co-ordination ", where it forms the unnamed group 9.BD.10 the only member.
In the mostly commonly used in the English-speaking classification of minerals according to Dana departments are pre-divided according to the type of group formation and possible additional anions. Here the hemimorphite is accordingly the only member of the unnamed group 56.01.02 within the subdivision: forms " group silicates Si2O7 Groups and O, OH, F, and H 2 O with cations in coordination ."
Education and Locations
Hemimorphite is likely to form secondary in the oxidation zones of galena - sphalerite - replacement deposits. Accompanying minerals occur in addition galena and sphalerite, you still Anglesit, Aurichalcit, calcite, cerussite, chrysocolla, Hydrozincite, Rosasit and Smithsonite.
Worldwide, Hemimorphite so far (as of 2012 ) can be detected at over 1400 localities. Apart from its type locality Baita the mineral still occurred in Romania in Dolea in Bihor county, and in Dognecea and Ocna de Fier in Caras -Severin county.
In Germany Hemimorphite found in many places in the Black Forest and Odenwald Baden -Württemberg; in several places in Lower and Upper Bavaria; in many places in Lower Saxony Harz; at Stolberg, in the Eifel, in Niederbergisches and Sauerland North Rhine -Westphalia; in some places in Rhineland -Palatinate and Saxony- Anhalt; in the Saxon Erzgebirge and Vogtland and in Gräfenroda in Thuringia.
In Austria, the mineral, especially in Carinthia ( Bleiberg, Gurktaler Alps, Hohe Tauern, Karawanken ), Lower Austria, Salzburg ( Hohe Tauern ), Styria ( Fischbacher Alps), North Tyrol and Vorarlberg was found.
In Switzerland, hemimorphite has so far been found mainly in the cantons of Graubünden and Valais, but also appeared in Seltisberg (Basel -Country), Malcantone (Ticino) and Bex ( Vaud) on.
The most massive crystals of up to 10 centimeters in length were discovered in Bisbee (Arizona ).
More Locations are, among others, 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, Caledonia, Norway, Peru, Poland, Portugal, Russia, Zambia, Sweden, Zimbabwe, Slovakia, Slovenia, Spain, South Africa, Tajikistan, Thailand, Tunisia, Czech Republic, Hungary, the United Kingdom ( UK), the United States of America ( USA) and Vietnam.
Crystal structure
Hemimorphite crystallizes in the orthorhombic space group Imm2 ( Raumgruppen-Nr. 44) with the lattice parameters a = 8.37 Å; b = 10.73 Å and c = 5.12 Å and two formula units per unit cell.
The crystal structure consists of double tetrahedra [ Si2O7 ] 6 -, which are linked via common corners, as well as from Zn2O6OH double tetrahedra over a shared hydroxide ion (OH ) - are connected. In the cavities formed by the tetrahedra larger the crystal water H2O is stored.
Use
Hemimorphite is used in local accumulation as zinc ore.