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Actinolite (Photo) [abbr. Act ]

Year of discovery: 1794 (World), 1885 (Japan)

Locality list: 688 localities of actinolite

• Ca₂Mg₅Si₈O₂₂(OH)₂
• (Ca,Na)₂(Mg,Fe²⁺,Al,Fe³⁺,Mn)₅(Si,Al)₈O₂₂(OH)₂, where Mg/(Mg+Fe)=0.5-0.9
• [][Ca²⁺₂][Mg²⁺₅][(OH)₂|(Si₄O₁₁)₂]^14-

• Class: Ca amphibole subgroup < w(OH,F,Cl)-dominant amphibole group < Amphibole supergroup
• Class: Inosilicate (Double chain) - Hydroxide
• Insoluble in: HCl, HNO₃, H₂SO₄
• Substitution pseudomorph: Replace pyroxenes such as Augite. (Uralite)
• Actinolite must be included in Tremolite, Mg end member of this series, by strict application of present nomenclature. However, this name was preserved because of its unique green color and difference of mode of occurrence.
• One of minerals called Asbestos.

• Mg/(Mg+Fe)=0-0.5: Ferro-actinolite (Series)
• Mg/(Mg+Fe)=0.9-1.0: Tremolite (Series)

• Ca => Mn: Mangano-cummingtonite
• Ca => Mg: anthophyllite, Cummingtonite, Proto-anthophyllite

• Ca₂ => CaMn: Parvo-manganotremolite

• MgSi => Al₂: Magnesio-hornblende (Series)

• Color: Green-Pale green
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent-Translucent

• Habit: Prismatic, Acicular, Bladed, Fibrous
• Aggregate: Columnar, Radial
• Twin: {100}

• Cleavage: Perfect on {110} (2 planes, 120 degree)
• Hardness: 5.5
• Density: 3.0

• System: Monoclinic
• Group: 2/m, B2/m, C2/m
• Lattice: a=9.9, b=18.2, c=5.3, β=104.6

Etymology: Aktis (Ray) in Greek