Amphibole (pronounced amfi-bowl) 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 ironand/or magnesiumin their structures. Amphiboles crystallize into two crystal systems, monoclinicand 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 pleochroismand 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, andesiteand 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 - amphibolos" meaning 'ambiguous') was used by RJ Haüy to include tremolite, actinolite, tourmaline and hornblende. The group was so named by Haüy in allusion to the protean variety, in composition and appearance, assumed by its minerals. 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
Of these, tremolite, hornblende, and crocidolite, as well as the important varieties,
asbestosand 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. Anthophylliteoccurs as brownish, fibrous or lamellar masses with hornblende in mica- schistat Kongsbergin Norwayand some other localities. An aluminous related species is known as gedriteand a deep green Russian variety containing little ironas 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
acicularcrystals 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- syeniteand phonolite.
Pargasite is a rare magnesium-rich amphibole with essential
sodium, usually found in ultramaficrocks. For instance, it occurs in uncommon mantle xenoliths, carried up by kimberlite. It is hard, dense, black and usually idiomorphic, with a red-brown pleochroismin petrographic thin section.
list of minerals
Amphiboliterock, and Amphibolite Facies
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, "Manual of Mineralogy", 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
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Amphibole — Am phi*bole ([a^]m f[i^]*b[=o]l), n. [Gr. amfi bolos doubtful, equivocal, fr. amfiba llein to throw round, to doubt: cf. F. amphibole. Ha[ u]y so named the genus from the great variety of color and composition assumed by the mineral.] (Min.) A… … The Collaborative International Dictionary of English
Amphibŏle — (Min.), so v.w. Hornblende … Pierer's Universal-Lexikon
Amphibole — Amphibole, Hornblende … Herders Conversations-Lexikon
amphibole — [am′fə bōl΄] n. [Fr < LL amphibolus, ambiguous < Gr amphibolos < amphiballein, to throw around, doubt < amphi , AMPHI + ballein, to throw: see BALL2] any of a group of rock forming minerals, as hornblende or actinolite, composed… … English World dictionary
Amphibole — Amphibolgruppe Amphibol, Fundort: Dolné Breziny, Slowakei Chemische Formel siehe Einzelminerale Mineralklasse Kettensilikate und Bandsilikate (Inosilikate) VIII/F.7 bis VIII/F.12 (nach Strunz) … Deutsch Wikipedia
amphibole — 1. amphibole [ ɑ̃fibɔl ] n. f. • 1787; gr. amphibolos « à double pointe » ♦ Géol. Groupe de silicates à deux clivages faciles et parfaits. Amphiboles alumineuses (ex. hornblende), non alumineuses (ex. actinote). Qui contient des amphiboles… … Encyclopédie Universelle
amphibole — /am feuh bohl /, n. Mineral. any of a complex group of hydrous silicate minerals, containing chiefly calcium, magnesium, sodium, iron, and aluminum, and including hornblende, tremolite, asbestos, etc., occurring as important constituents of many… … Universalium
Amphibole — Am|phi|bo|le 〈Pl.; Min.〉 Gruppe weitverbreiteter gesteinsbildender Minerale, z. B. Hornblende [→ Amphibolie] * * * Amphibole, Singular Amphibol der, s, Gruppe sehr verbreiteter gesteinsbildender Calcium Magnesium oder Natrium Magnesium… … Universal-Lexikon
Amphibole — Motif cristallin élémentaire des amphiboles Les amphiboles sont une famille de minéraux, silicates de fer, de calcium ou de magnésium. Elles cristallisent dans les systèmes orthorhombique et monoclinique en prismes très allongés, avec un clivage… … Wikipédia en Français
amphibole — noun a mineral or mineral variety belonging to the amphibole group • Hypernyms: ↑mineral • Hyponyms: ↑nephrite, ↑actinolite, ↑anthophyllite, ↑asbestos, ↑hornblende • Member Holonyms: ↑ … Useful english dictionary