Amphibole
The amphiboles are a group of minerals from the silicate class, inosilicate group. The name of amphibole derives from the Greek ἀμφίβολος - amphibolos, which means ambiguous, alluding to the changing varieties, in composition and appearance, that these minerals present.
Chemical Structure
Chemically they are metasilicates of calcium, magnesium and iron. The fundamental structural unit of amphiboles is the silicon oxygen tetrahedron (SiO4) linked in the form of long double chains. The chemical formula of each amphibole mineral is the result of metal substitutions in the double chain: RSi4O11.
Features
The most common minerals in basic metamorphic and plutonic rocks are hornblende and actinolite. They are the fundamental minerals of magmatic rocks, and an essential component of amphibolite. They are black or dark green in color and their appearance is glassy or milky, in thin section they present moderate relief, slight pleochroism, low interference colors and in basal section they present cleavage angles of 124° and 56° as a distinctive characteristic.
Amphibole minerals
There are many species and varieties, some of the most important can be grouped into four subgroups:
Mg-Mn-Fe-Li clinoamphiboles
Name of mineral Chemical formula Clinoferroholmquistita Li2[2+)3Al2Yes8O22(OH,F)2 Cummingtonite or Antholita Mg7Yeah.8O22(OH)2 Grunerita (Federal2+)7Yeah.8O22(OH)2 Manganocummingtonita or Tirodita (Mn)2Mg5Yeah.8O22(OH)2 Manganogrunerita (Mn)2(Federal2+)5Yeah.8O22(OH)2
Cline Amphiboles of Calcium
Name of mineral Chemical formula Actinolita Ca2(Mg, Fe2+)5Yeah.8O22(OH)2 Baroisita ()NaCa[Mg3(Al, Fe3+)2](Yes7(a)O22(OH)2 Cannilloita Ca Ca2(Mg4Al)(Yes5Al3O22(OH)2 Edenita NaCa2Mg5Yes7(a)O22(OH)2 Ferroactinolita ()Ca2(Federal2+)5Yeah.8O22(OH)2 Ferroedenita NaCa2(Federal2+)5Yes7(a)O22(OH)2 Ferritschermakita Ca2[Mg3(Federal3+)2](Yes6Al2O22(OH)2 Ferrobarroisita ()NaCa[(Feb)2+)3AlFe3+](Yes7(a)O22(OH)2 Ferrohornblenda ()Ca2[2+)4Al.7(a)O22(OH)2 Ferrokaersutita NaCa2[2+)4Ti4+](Yes6Al2O23(OH) Ferropargasita NaCa2[2+)4Al.6Al2O22(OH)2 Ferrorichterita Na2Ca(Fe2+)5Yeah.8O22(OH)2 Ferrotschermakita ()Ca2[2+)3AlFe3+](Yes6Al2O22(OH)2 Ferrowinchita ()NaCa[(Feb)2+)4Yeah.8O22(OH)2 Fluorocanilloite Ca Ca2(Mg4Al)(Yes5Al3)8O22F2 Fluoroedenite NaCa2Mg5Yes7(a)O22F2 Fluoropotasicrichterite KNaCaMg5Yeah.8O22F2 Hastingsita NaCa2[2+)4Fe3+](Yes6Al2O22(OH)2 Kaersutita NaCa2(Mg4AlTi4+)(Yes6Al2O22O2 Catoforita Na2Ca[Fe2+)4Al.7(a)O22(OH)2 Magnesiohastingsita or Tibergita NaCa2(Mg4Fe3+)(Yes6Al2O22(OH)2 Magnesiumhornblenda ()Ca2[Mg4(Al, Fe3+)7(a)O22(OH)2 Magnesiumkatophorita NaNaCa(Mg4Al)(Yes7(a)O22(OH)2 Magnesydaagaite NaCa2[Mg3(Federal3+, Al)2](Yes5Al3O22(OH)2 Magnesiotaramita NaNaCa(Mg3AlFe3+)(Yes6Al2O22(OH)2 Pargasita NaCa2(Mg4Al)(Yes6Al2O22(OH)2 Parvo-manganotremolita (CaMn)Mg5Yeah.8O22(OH)2 Potásico-Ferrisadanagaita KCa2[2+)3(Federal3+)2](Yes5Al3O22(OH)2 Potassicpargasita KCa2(Mg4Al)(Yes6Al2O22(OH)2 Richterita or Isabellita Na(CaNa)Mg5Yeah.8O22(OH)2 Taramita Na2Ca(Fe2+)3AlFe3+Yes6Al2O22(OH)2 Tremolita, Calamita, Peponita or Sebesita ()Ca2Mg5Yeah.8O22(OH)2 Tschermakita Ca2(Mg3AlFe3+)(Yes6Al2O22(OH)2 Eckrita or Winchita ()NaCa[Mg4Yeah.8O22(OH)2
Cline Amphibole Sodium
Name of mineral Chemical formula Aluminotaramita Na2Ca(Fe2+)3Al2Yes6Al2O22(OH)2 IMA2007-015 K(Ca, Na)2+3Al2(OH)2- Yeah.6Al2O22)
Mg-Fe-Mn-Li Orthoamphiboles
Name of mineral Chemical formula Anthophilite (Mg)7Yeah.8O22(OH)2 Ferroantofilita (Federal)2+)7Yeah.8O22(OH)2 Ferrogedrita (Federal)2+)5Al2Yes6Al2O22(OH)2 Gedrita or Bidalotita (Mg)5Al2Yes6Al2O22(OH)2 Holmquistita Li2(Mg3Al2Yes8O22(OH)2 Protoferro-antofilita (Federal2+)7Yeah.8O22(OH)2 Protomangano-ferro-antofilita (Mn2+)2(Federal2+)5Yeah.8O22(OH)2 Sodium-ferro-antofilite Na(Fem2+)7Yes7(a)O22(OH)2 Sodium-ferro-gedrita Na(Fem2+)5Al2Yes5Al3O22(OH)2 Sodicantofilita NaMg7Yes7(a)O22(OH)2 Sodicgedrita NaMg6Al(Yes6Al2O22(OH)2
- Antofilite (Mg, Fe)7Yeah.8O22(OH)2
- Tremolita Ca2Mg5Yeah.8O22(OH)2
- Actinolita Ca2(Mg, Fe)5Yeah.8O22(OH)2
- Cummingtonita Fe2Mg5Yeah.8O22(OH)2
- Grunerita Fe7Yeah.8O22(OH)2
- Hornblenda Ca2(Mg, Fe, Al)5(Al, Si)8O22(OH)2
- Glaucofana Na2(Mg, Fe)3Al2Yeah.8O22(OH)2
- Riebeckita Na2Fe2+3Fe3+2Yeah.8O22(OH)2
- Arfvedsonita Na3Fe2+4Fe3+Yeah.8O22(OH)2
- Crocidolita Na2Fe2+3Fe3+2Yeah.8O22(OH)2
- Richterita Na2Ca(Mg, Fe)5Yeah.8O22(OH)2
- Pargasita NaCa2Mg3Fe2+Yeah.6Al3O22(OH)2
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