For the logical fallacy, see
Amphibology. Amphibole defines an important group of generally dark-colored rock-forming
inosilicate minerals, composed of double chain SiO4 tetrahedra, linked at the vertices and generally containing
ions of
iron and/or
magnesium in their structures. Amphiboles crystallize into two crystal systems,
monoclinic and
orthorhombic. In chemical composition and general characteristics they are similar to the
pyroxenes. The chief differences between amphiboles and pyroxenes are that (i) they contain essential hydroxyl (OH) or halogene (F, Cl) and (ii) the basic structure is a double chain of tetrahedra (as opposed to the single chain structure of pyroxene). Most apparent, in hand specimens, is that amphiboles form oblique cleavage planes (at around 120 degrees), whereas pyroxenes have cleavage angles of approximately 90 degrees. Amphiboles are also specifically less dense than the corresponding pyroxenes. In optical characteristics, many amphiboles are distinguished by their stronger
pleochroism and by the smaller angle of extinction (Z angle c) on the plane of symmetry. Amphiboles are the primary constituent of
amphibolites.
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Die Amphibolgruppe (kurz: Amphibole) umfasst
Silikate, die sich strukturell durch Doppelketten aus eckenverknüpften SiO4-Tetraedern auszeichnen und deren Zusammensetzung der folgenden verallgemeinerten Summenformel genügt: A0-1B2C5T8O22(OH)2. In dieser Strukturformel repräsentieren die Großbuchstaben A,B,C und T unterschiedliche Positionen in der Amphibolstruktur. Sie werden durch folgende Kationen belegt: A: Leerstellen, Na+, K+, Ba+, Sr+, Ca+, Li+B: Ca2+, Na+, Mg2+, Fe2+, Mn2+, Li+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Mg2+, Pb2+, Cu, Zr, Mn3+, Cr3+, V, Fe3+, C: Mg2+, Fe2+, Mn2+, Li+, Al3+, Zn2+, Ni2+, Co2+, Ti4+, Fe3+, V, Cr3+, Mn3+, Zr, T: Si4+, Al3+, Ti4+
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