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For the logical fallacy, see Amphibology.


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Amphibole (Hornblende)


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.

Amphiboles are minerals of either igneous or metamorphic origin; in the former case occurring as constituents (hornblende) of igneous rocks, such as granite, diorite, andesite and others. Those of metamorphic origin include examples such as those developed in limestones by contact metamorphism (tremolite) and those formed by the alteration of other ferromagnesian minerals (hornblende). Pseudomorphs of amphibole after pyroxene are known as uralite.

The name amphibole (Greek αμφιβολος/amfibolos meaning 'ambiguous') was used by RJ Haüy to include tremolite, actinolite and hornblende. This term has since been applied to the whole group. Numerous sub-species and varieties are distinguished, the more important of which are tabulated below in three series. The formulae of each will be seen to be built on the general double-chain silicate formula RSi4O11.

Amphibole groups

Orthorhombic Series Monoclinic Series Of these, tremolite, hornblende, and crocidolite, as well as the important varieties, asbestos and jade, are treated under their own headings. Brief mention need only be made of some of the others. Naturally, on account of the wide variations in chemical composition, the different members vary considerably in properties and general appearance.

Anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica-schist at Kongsberg in Norway and some other localities. An aluminous related species is known as gedrite and a deep green Russian variety containing little iron as kupfferite.

Hornblende is an important constituent of many igneous rocks. It is also an important constituent of amphibolites formed by metamorphism of basalt.

Actinolite is an important and common member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish-green color. It occurs frequently as a constituent of greenschists. The name (from Greek ακτις/aktis, a 'ray' and λιθος/lithos, a 'stone') is a translation of the old German word Strahlstein (radiated stone).

Glaucophane, crocidolite, riebeckite and arfvedsonite form a somewhat special group of alkali-amphiboles. The first two are blue fibrous minerals, with glaucophane occurring in blueschists and crocidolite (blue asbestos) in ironstone formations, both resulting from dynamo-metamorphic processes. The latter two are dark green minerals, which occur as original constituents of igneous rocks rich in sodium, such as nepheline-syenite and phonolite.

Pargasite is a rare magnesium-rich amphibole with essential sodium, usually found in ultramafic rocks. For instance, it occurs in uncommon mantle xenoliths, carried up by kimberlite. It is hard, dense, black and usually idiomorphic, with a red-brown pleochroism in petrographic thin section.

See also

References

  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
Amphibology or amphiboly (from the Greek amphibolia) is an ambiguous grammatical structure in a sentence.

Some examples:

Teenagers shouldn't be allowed to drive. It's getting too dangerous on the streets.

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The silicate minerals make up the largest and most important class of rock-forming minerals. They are classified based on the structure of their silicate ion group.

Subclasses:

Nesosilicates or Isosilicates

Nesosilicates (or orthosilicates
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A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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3, 4, 6
(amphoteric oxide)
Electronegativity 1.83 (Pauling scale)
Ionization energies
(more) 1st: 762.5 kJmol−1
2nd: 1561.9 kJmol−1
3rd: 2957 kJmol−1

Atomic radius 140 pm
Atomic radius (calc.
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Magnesium has the symbol Mg, the atomic number 12, and an atomic mass of 24.31. Magnesium is the ninth most abundant element in the universe by mass. It constitutes about 2% of the Earth's crust by mass, and it is the third most abundant element dissolved in seawater.
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monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a parallelogram as base.
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orthorhombic crystal system is one of the 7 lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its lattice vectors by two different factors, resulting in a rectangular prism with a rectangular base (a by b
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The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rocks. They share a common structure comprised of single chains of silica tetrahedra and they crystalise in the monoclinic and orthorhombic system.
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Amphibolite (IPA: /æmˈfɪbəlɑɪt/, /amˈfɪbəlʌɪt/
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Hornblende is a complex inosilicate series of minerals. Hornblende is not a recognized mineral, in its own right but the name is used as a general or field term, to refer to a dark amphibole.
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Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
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Granite (IPA: /ˈɡrænɪt/) is a common and widely occurring type of intrusive, felsic, igneous rock. Granites are usually medium to coarsely crystalline, occasionally with some individual crystals larger than the
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Diorite (IPA: /ˈdʌɪərʌɪt/) is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene.
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Andesite (IPA: /ˈandəsʌɪt/) is an igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture.
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Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3). Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers
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Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i.e without melting. There will be mineralogical, chemical and crystallographic changes.
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Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz.
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Hornblende is a complex inosilicate series of minerals. Hornblende is not a recognized mineral, in its own right but the name is used as a general or field term, to refer to a dark amphibole.
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Actinote redirects here. For the brush-footed butterfly genus, see Actinote (butterfly).


Actinolite is an inosilicate mineral with the chemical formula
Ca2(Mg,Fe)5Si8O22(OH)2


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Ancient Greek refers to the second stage in the history of the Greek language[1] as it existed during the Archaic (9th–6th centuries BC) and Classical (5th–4th centuries BC) periods in Greece.
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René Just Haüy (February 28, 1743 – June 3, 1822) was a French mineralogist, commonly styled the Abbé Haüy after he was made an honorary canon of Notre Dame.

Biography

Haüy was born at Saint-Just-en-Chaussée, in the département of Oise.
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silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate ("fluorosilicate"), [SiF6]2−
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Anthophyllite is an amphibole mineral: (Mg, Fe)7Si8O22(OH)2, magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are used as asbestos.
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Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz.
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Actinote redirects here. For the brush-footed butterfly genus, see Actinote (butterfly).


Actinolite is an inosilicate mineral with the chemical formula
Ca2(Mg,Fe)5Si8O22(OH)2


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Cummingtonite or magnesium iron silicate hydroxide is a metamorphic amphibole with the chemical composition (Mg,Fe)7Si8O22(OH)2.
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Grunerite is a mineral of the amphibole group of minerals with formula Fe7Si8O22(OH)2. It is the iron endmember of the grunerite-cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals.
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Hornblende is a complex inosilicate series of minerals. Hornblende is not a recognized mineral, in its own right but the name is used as a general or field term, to refer to a dark amphibole.
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