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   » » Wiki: Amphibole
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Amphibole () is a group of inosilicate , forming prism or needlelike crystals, composed of double chain , linked at the vertices and generally containing of and/or in their structures. It's IMA symbol is Amp. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups. Mindat, Amphibole Supergroup

Amphiboles crystallize into two crystal systems, and .
(1993). 047157452X, Wiley. 047157452X
In chemical composition and general characteristics they are similar to the . The chief differences from pyroxenes are that (i) amphiboles contain essential hydroxyl (OH) or halogen (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. Amphiboles are the primary constituent of .

In rocks
Amphiboles are minerals of either or origin. Amphiboles are more common in intermediate to igneous rocks than in igneous rocks, because the higher and dissolved water content of the more evolved magmas favors formation of amphiboles rather than pyroxenes.
(2022). 9780195106916, Oxford University Press.
The highest amphibole content, around 20%, is found in .
(2022). 9780470387740, J. Wiley.
is widespread in igneous and metamorphic rocks and is particularly common in and . Calcium is sometimes a constituent of naturally occurring amphiboles. Amphilotes of metamorphic origin include those developed in by contact metamorphism () and those formed by the alteration of other ferromagnesian minerals (such as hornblende as an alteration product of pyroxene). of amphibole after pyroxene are known as .

History and etymology
The name amphibole derives from (, ), implying ambiguity. The name was used by René Just Haüy to include tremolite, and . 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 two series. The formulae of each will be seen to be built on the general double-chain formula RSi4O11.

Four of the amphibole minerals are among the minerals commonly called . These are: anthophyllite, riebeckite, the cummingtonite/grunerite series, and the actinolite/tremolite series. The cummingtonite/grunerite series is often termed amosite or "brown asbestos", and riebeckite is known as crocidolite or "blue asbestos". These are generally called amphibole asbestos.US Geological Survey, Asbestos, accessed 20 July 2015. Mining, manufacture and prolonged use of these minerals can cause serious illnesses.

Mineral species

Chemical formula
Orthorhombic series Monoclinic series

On account of the wide variations in chemical composition, the different members vary considerably in properties and general appearance.

occurs as brownish, fibrous or lamellar masses with hornblende in - at in and some other localities. An aluminous related species is known as and a deep green variety containing little as .

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

is an important and common member of the monoclinic series, forming radiating groups of crystals of a bright green or greyish-green color. It occurs frequently as a constituent of . The name (from ἀκτίς, ἀκτῖνος/aktís, aktînos, a 'ray' and λίθος/líthos, a 'stone') is a translation of the old word Strahlstein (radiated stone).

, , and form a somewhat special group of alkali-amphiboles. The first two are blue fibrous minerals, with glaucophane occurring in 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 - and .

is a rare magnesium-rich variety of hornblende with essential , usually found in rocks. For instance, it occurs in uncommon mantle , carried up by . It is hard, dense, black and usually automorphic, with a red-brown in .


See also
  • List of minerals
  • Classification of silicate minerals


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