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