amphibole
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Amphibole () is a group of
inosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thi ...

inosilicate
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (20 ...

mineral
s, forming prism or needlelike crystals, composed of double chain
tetrahedra In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of spac ...

tetrahedra
, linked at the vertices and generally containing
ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical property, physical or ...
s of
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...

iron
and/or
magnesium Magnesium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

magnesium
in their structures. It's IMA
symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), meanin ...
is Amp. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The
International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy Mineralogy is a subject of geology specializing in the scientific study of the ...
currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups.


Mineralogy

Amphiboles crystallize into two crystal systems,
monoclinic In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek words ''crystallon'' "cold drop, froze ...

monoclinic
and
orthorhombicIn crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, resul ...

orthorhombic
. In chemical composition and general characteristics they are similar to the
pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium Calcium is a ...
s. 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
amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase. Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz. It ...
s.


In rocks

Amphiboles are minerals of either
igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
or metamorphic origin. Amphiboles are more common in intermediate to
felsic In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes ...
igneous rocks than in
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole Amphibole () is a group of Silic ...
igneous rocks, because the higher
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

silica
and dissolved water content of the more
evolved Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are passed on from parent to offsp ...
magmas favors formation of amphiboles rather than pyroxenes. The highest amphibole content, around 20%, is found in
andesite Andesite ( or ) is an extrusive volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geology), rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being o ...
s.
Hornblende Hornblende is a complex inosilicate series of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock ...

Hornblende
is widespread in igneous and metamorphic rocks and is particularly common in
syenite leucocratic variety of nepheline syenite from Sweden">nepheline.html" ;"title="leucocratic variety of nepheline">leucocratic variety of nepheline syenite from Sweden (särnaite) Syenite is a coarse-grained Intrusion, intrusive igneous rock with ...

syenite
s and
diorite Orbicular diorite from Corsica (corsite) Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metal ...
s. Calcium is sometimes a constituent of naturally occurring amphiboles. Amphilotes of metamorphic origin include those developed in
limestone Limestone is a common type of carbonate rock, carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science), crystal forms of calcium carbonate (). Limestone forms ...

limestone
s by contact metamorphism (
tremolite Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in Dolomite (mineral), dolomite and quartz. Tremolite forms a series with a ...

tremolite
) and those formed by the alteration of other ferromagnesian minerals (such as hornblende as an alteration product of pyroxene).
Pseudomorph In mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and mineralized artifact (archaeology), artifac ...

Pseudomorph
s of amphibole after pyroxene are known as uralite.


History and etymology

The name ''amphibole'' derives from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
(, ), implying ambiguity. The name was used by to include tremolite,
actinolite Actinolite is an amphibole Amphibole () is a group of Silicate minerals, inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedron, tetrahedra, linked at the vertices and generally containing ions of ir ...

actinolite
and
hornblende Hornblende is a complex inosilicate series of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock ...

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 two series. The formulae of each will be seen to be built on the general double-chain
silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they unde ...
formula RSi4O11. Four of the amphibole minerals are among the minerals commonly called
asbestos Asbestos (pronounced: or ) is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into ...
. 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. Mining, manufacture and prolonged use of these minerals can cause serious illnesses.


Mineral species


Chemical formula

Orthorhombic series *
Anthophyllite Anthophyllite is an amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite ar ...

Anthophyllite
, (Fe,Mg)7Si8O22(OH)2 * Holmquistite, Li2Mg3Al2Si8O22(OH)2 * Ferrogedrite, Fe2+5Al4Si6O22(OH)2 Monoclinic series * Tremolite, Ca2Mg5Si8O22(OH)2 * Actinolite, Ca2(Mg,Fe)5Si8O22(OH)2 * Cummingtonite, Fe2Mg5Si8O22(OH)2 * Grunerite, Fe7Si8O22(OH)2 *
Hornblende Hornblende is a complex inosilicate series of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock ...

Hornblende
, (K,Na)0-1(Ca,Na,Fe,Mg)2(Mg,Fe,Al)5(Al,Si)8O22(OH)2 * Glaucophane, Na2(Mg,Fe)3Al2Si8O22(OH)2 * Riebeckite (or Crocidolite), Na2Fe2+3Fe3+2Si8O22(OH)2 * Arfvedsonite, Na3Fe2+4Fe3+Si8O22(OH)2 * Richterite, Na2Ca(Mg,Fe)5Si8O22(OH)2 * Pargasite, NaCa2Mg3Fe2+Si6Al3O22(OH)2 * Winchite, (CaNa)Mg4(Al,Fe3+)Si8O22(OH)2 * Edenite, NaCa2Mg5(Si7Al)O22(OH)2 * Kaersutite, NaCa2(Mg3Ti4+Al)(Si6Al2)O22(OH)2


Descriptions

On account of the wide variations in chemical composition, the different members vary considerably in properties and general appearance.
Anthophyllite Anthophyllite is an amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite ar ...

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 Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...

iron
as kupfferite.
Hornblende Hornblende is a complex inosilicate series of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock ...

Hornblende
is an important constituent of many igneous rocks. It is also an important constituent of
amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase. Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz. It ...
s formed by metamorphism of basalt. Actinolite is an important and common member of the monoclinic series, forming radiating groups of Crystal habit, acicular crystals of a bright green or greyish-green color. It occurs frequently as a constituent of greenschists. The name (from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
''ἀκτίς, ἀκτῖνος/aktís, aktînos'', a 'ray' and ''λίθος/líthos'', a 'stone') is a translation of the old German language, 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 leucocratic variety of nepheline syenite from Sweden">nepheline.html" ;"title="leucocratic variety of nepheline">leucocratic variety of nepheline syenite from Sweden (särnaite) Syenite is a coarse-grained Intrusion, intrusive igneous rock with ...

syenite
and phonolite. Pargasite is a rare magnesium-rich variety of hornblende with essential sodium, usually found in ultramafic rocks. For instance, it occurs in uncommon Mantle (geology), mantle xenoliths, carried up by kimberlite. It is hard, dense, black and usually Rock microstructure#Crystal shapes, automorphic, with a red-brown pleochroism in Petrography, petrographic thin section.


See also

* List of minerals * Classification of silicate minerals


Notes


References

* C. Michael Hogan. 2010
''Calcium''. eds. A.Jorgensen, C. Cleveland. Encyclopedia of Earth
National Council for Science and the Environment. * Cornelius S. Hurlbut and Cornelis Klein. 1985. ''Manual of Mineralogy'', 20th ed., John Wiley and Sons, New York {{Authority control Inosilicates Asbestos