HORNBLENDE
The
Amphibole Group
of Minerals

TREMOLITE


TREMOLITE

FLUORRICHTERITE

ANTHOPHYLLITE

The amphibole minerals are inosilicates of the general formula XY2Z5(Si, Al, Ti)8O22(OH, F)2. The X represents large ions such as sodium or potassium and this site can be left vacant. The Y can be populated by sodium, calcium, iron (+2), lithium, manganese (+2), aluminum and/or magnesium and more rarely zinc, nickel, or cobalt. The Z can be filled by ions such as Iron (+3), manganese (+3), chromium (+3), aluminum, titanium (+4), iron (+2), lithium and manganese (+2). Most amphiboles are monoclinic, 2/m; but members of the Anthophyllite Subgroup are orthorhombic, 2/m 2/m 2/m. The rather complex possibilities of formulas does lead to a lot of variety in the amphibole group. Compare the formulas of these common amphiboles:

  • Actinolite Ca2(Mg, Fe+2)5 Si8O22(OH)2
  • Anthophyllite (Mg, Fe)7 Si8O22(OH)2
  • Arfvedsonite Na3(Fe+2)4Fe+3 Si8O22(OH)2
  • Cummingtonite Mg7 Si8O22(OH)2
  • Edenite NaCa2Mg5 Si8O22(OH)2
  • Fluorrichterite Na(CaNa)Mg5 Si8O22F2
  • Glaucophane Na2(Mg3Al2) Si8O22(OH)2
  • The Hornblende Series Ca2(Mg, Fe+2)4 (Al, Fe+3)Si7AlO22(OH)2
  • Riebeckite Na2Fe+23 Fe+32Si8O22(OH)2
  • Tremolite Ca2Mg5 Si8O22(OH)2

The amphiboles represent the majority of the double-chained inosilicates. They are common rock forming minerals and are present in most metamorphic and many igneous rocks. Amphiboles form at lower temperatures with the presence of water; always at the expense of the their single chained cousins, the pyroxenes. Petrologists can use the presence of amphiboles to gauge the original water content of the rock forming melt. Pyroxenes only form when water is scarce. The amphiboles are a rather large group with over 60 recognized members; mostly because of chemical differences.
These are the minerals of the Amphibole Group:

    Cummingtonite Subgroup (Fe-Mg-Li Clinoamphiboles):

    • Clinoferroholmquistite (Lithium Iron Aluminum Silicate Hydroxide)
    • Clinoholmquistite (Lithium Magnesium Aluminum Silicate Hydroxide)
    • Cummingtonite (Iron Magnesium Silicate Hydroxide)
    • Dannemorite (Sodium Magnesium Aluminum Silicate Hydroxide)
    • Grunerite (Iron Silicate Hydroxide)
    • Holmquistite (Lithium Magnesium Aluminum Silicate Hydroxide)
    • Magnesiocummingtonite (Magnesium Iron Silicate Hydroxide)
    • Sodic-ferri-clinoferroholmquistite (Lithium Iron Magnesium Silicate Hydroxide)
    • Tirodite (Manganese Magnesium Silicate Hydroxide)

    Anthophyllite Subgroup (Fe-Mg-Li Orthoamphiboles):

    • Anthophyllite (Magnesium Iron Silicate Hydroxide)
    • Ferro-anthophyllite (Iron Silicate Hydroxide)
    • Ferrogedrite (Iron Aluminum Silicate Hydroxide)
    • Ferroholmquistite (Lithium Iron Aluminum Silicate Hydroxide)
    • Gedrite (Magnesium Aluminum Silicate Hydroxide)
    • Protoferro-anthophyllite (Iron Manganese Magnesium Silicate Hydroxide)
    • Protomangano-ferro-anthophyllite (Manganese Iron Magnesium Silicate Hydroxide)
    • Sodicanthophyllite (Sodium Magnesium Silicate Hydroxide)
    • Sodic-ferro-anthophyllite (Sodium Iron Silicate Hydroxide)
    • Sodic-ferrogedrite (Sodium Iron Aluminum Silicate Hydroxide)
    • Sodicgedrite (Sodium Magnesium Aluminum Silicate Hydroxide)

    Tremolite Subgroup (Ca Amphiboles):

    • Actinolite (Calcium Magnesium Iron Silicate Hydroxide)
    • Edenite (Sodium Calcium Magnesium Iron Aluminum Silicate Hydroxide)
    • Ferro-actinolite (Calcium Iron Silicate Hydroxide)
    • Ferro-edenite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Ferrohornblende (Calcium Iron Aluminum Silicate Hydroxide)
    • Ferrokaersutite (Sodium Calcium Iron Titanium Aluminum Silicate Hydroxide)
    • Ferropargasite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Ferrotschermakite (Calcium Iron Aluminum Silicate Hydroxide)
    • Fluorocannilloite (Calcium Magnesium Aluminum Silicate Fluoride)
    • Hastingsite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Hornblende (Calcium Sodium Magnesium Iron Aluminum Silicate Hydroxide)
    • Kaersutite (Sodium Calcium Magnesium Titanium Aluminum Silicate Hydroxide)
    • Magnesiohastingsite (Sodium Calcium Magnesium Iron Aluminum Silicate Hydroxide)
    • Magnesiohornblende (Calcium Magnesium Aluminum Iron Silicate Hydroxide)
    • Magnesiosadanagaite (Sodium Calcium Magnesium Aluminum Iron Silicate Hydroxide)
    • Pargasite (Sodium Calcium Magnesium Aluminum Silicate Hydroxide)
    • Potassic-magnesiosadanagaite (Potassium Sodium Calcium Magnesium Aluminum Iron Silicate Hydroxide)
    • Potassicpargasite (Potassium Sodium Calcium Magnesium Iron Aluminum Silicate Hydroxide Fluoride)
    • Potassicsadanagaite (Potassium Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Tremolite (Calcium Magnesium Iron Silicate Hydroxide)
    • Tschermakite (Calcium Magnesium Aluminum Iron Silicate Hydroxide)

    Richterite Subgroup (Ca-Na Clinoamphiboles):

    • Barroisite (Calcium Sodium Magnesium Aluminum Iron Silicate Hydroxide)
    • Ferrobarroisite (Calcium Sodium Iron Aluminum Silicate Hydroxide)
    • Ferrorichterite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Ferrowinchite (Calcium Sodium Iron Aluminum Silicate Hydroxide)
    • Fluorrichterite (Sodium Calcium Magnesium Silicate Fluoride)
    • Katophorite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Magnesiokatophorite (Sodium Calcium Magnesium Aluminum Iron Silicate Hydroxide)
    • Magnesiotaramite (Sodium Calcium Magnesium Aluminum Iron Silicate Hydroxide)
    • Potassic-fluorrichterite (Potassium Sodium Calcium Magnesium Silicate Fluoride)
    • Richterite (Sodium Calcium Magnesium Silicate Hydroxide)
    • Taramite (Sodium Calcium Iron Aluminum Silicate Hydroxide)
    • Winchite (Calcium Sodium Magnesium Aluminum Iron Silicate Hydroxide)

    Glaucophane Subgroup (Alkali Amphiboles):

    • Arfvedsonite (Sodium Iron Magnesium Silicate Hydroxide)
    • Eckermannite (Sodium Magnesium Aluminum Silicate Hydroxide)
    • Ferro-eckermannite (Sodium Iron Aluminum Silicate Hydroxide)
    • Ferroglaucophane (Sodium Iron Aluminum Silicate Hydroxide)
    • Fluoro-ferroleakeite (Sodium Iron Lithium Silicate Fluoride)
    • Glaucophane (Sodium Magnesium Aluminum Silicate Hydroxide)
    • Kornite (Sodium Potassium Magnesium Manganese Lithium Silicate Hydroxide)
    • Kozulite (Sodium Manganese Iron Aluminum Silicate Hydroxide)
    • Leakeite (Sodium Magnesium Iron Lithium Silicate Hydroxide)
    • Magnesio-arfvedsonite (Sodium Magnesium Iron Silicate Hydroxide)
    • Magnesioriebeckite (Sodium Magnesium Iron Silicate Hydroxide)
    • Nyboite (Sodium Magnesium Aluminum Silicate Hydroxide)
    • Riebeckite (Sodium Iron Silicate Hydroxide)
    • Ungarettiite (Sodium Manganese Silicate Oxide)

    The mineral Joesmithite, PbCa2(Mg, Fe+2, Fe+3)5Si6 Be2O22(OH)2, is a similar inosilicate that is sometimes included in the Amphibole Group.
Popular Members of the Silicates Class
 

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