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Amphibole defines an important group of dark-colored rock-forming silicate minerals composed of double chain SiO4 tetrahedra linked at the vertices and generally containing ions of iron and/ or magnesium in their structures. In chemical composition and general characteristics they are very similar to the pyroxenes and like them fall into three series according to their system of crystallization. The chief difference between amphiboles and pyroxenes is in cleavage: amphiboles form oblique cleaveage plains, while pyroxenes have cleavages of approximately 90 degrees. Amphiboles are also specifically less dense than the corresponding pyroxenes, and in their optical characteristics they are distinguished by their stronger pleochroism and by the wider angle of extinction on the plane of symmetry. Amphiboles are the primary constituent of amphibolites.
Amphiboles are minerals of either original or secondary origin; in the former case occurring as constituents ( hornblende) of igneous rocks, such as granite, diorite, andesite and others. Those of secondary origin have either been developed in limestones by contact metamorphismMetamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. without melting, in response to new conditions of pressure and/or temperature, and/or introduction of fluids. Metamorphism produced with incr ( tremolite) or have resulted by the alteration of augiteAugite is a mafic mineral described chemically as (Ca, Na)(Mg, Fe, Al)(Al, Si)O or calcium sodium magnesium iron aluminium silicate. Structurally, it is a solid solution of the pyroxene group which also contains diopside and hedenbergite. The crystals are by dynamo-metamorphism ( actinoliteThere is also a community named Actinolite,_Ontario in Canada. metadiabase intrudes light granitic gneiss Actinolite is an inosilicate mineral with the chemical formula Ca(MgFe)SiO(OH) Mineralogy Actinolite is an intermediate member in a series between tr). Pseudomorphs of amphibole after pyroxene are known as uralite .
The name amphibole ( GreekThe word Greek has a number of meanings relating to Greece, including: Architecture of Ancient Greece Art in Ancient Greece Greek alphabet Greek colonies Cuisine of Greece Ethnic Greek Greco-Turkish relations Greece Hellenes History of Greece History of M amfibolos, "ambiguous") was used by RJ HaüyRene Just Hauy ( February 28, 1743 June 3, 1822), French mineralogist, commonly styled the Abbe Hauy from being an honorary canon of Notre Dame, was born at St Just, in the department of Oise. His parents were in a humble rank of life, and were only enabl 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 conform to the general meta silicate formula RSiO3.
Orthorhombic Series
Monoclinic Series
Anorthic Series
Of these, tremolite, hornblende, and crocidolite, as well as the important varieties, asbestos and jade, are treated under their own headings. Brief mention only need be here 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; the specific gravity, for example, varies from 2.9 in tremolite to 3.8 in aenigmatite .
Anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica- schist at Kongsberg in Norway and some other localities. An aluminous variety is known as gedrite , and a deep green Russian variety containing little iron as kupfferite .Actinolite is an important 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 crystalline schists. The name (from aktis, a ray, and 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 two former are blue fibrous minerals occurring in crystalline schists, and are the result of dynamo-metamorphic processes; the two latter are dark green minerals which occur as original constituents of igneous rocks rich in soda, such as nepheline- syenite and phonolite.
Aenigmatite and its variety cossyrite are rare minerals forming constituents of igneous rocks of the nepheline-syenite and phonolite groups.