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Kaersutite in tuff.jpg
Category Inosilicate
(repeating unit)
Strunz classification 9.DE.10
Dana classification 66.01.03a.18
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
Color Dark brown to black - yellow-brown, green-brown, or red-brown in thin section
Crystal habit Prismatic phenocrysts, granular aggregates
Twinning Simple or multiple twinning parallel to {100}
Cleavage Perfect on {110}, intersecting at 56° and 124°
Tenacity Brittle
Mohs scale hardness 5 - 6
Luster Vitreous
Streak Pale brownish-grey
Diaphaneity Semitransparent
Specific gravity 3.20 - 3.28
Optical properties Biaxial (-)
Refractive index nα = 1.670 - 1.689 nβ = 1.690 - 1.741 nγ = 1.700 - 1.772
Birefringence δ = 0.030 - 0.083
Pleochroism Strong; X = yellow, yellow-brown; Y = red, red-brown; Z = deep brown, dark red-brown.
2V angle 66 - 82°
References [1][2][3][4]

Kaersutite is a dark brown to black double chain calcic titanium bearing amphibole mineral with formula: NaCa2(Mg3Ti4+Al)(Si6Al2)O22(OH)2.

Ferro-kaersutite is the divalent iron rich endmember of the kaersutite group, with the iron replacing magnesium in the structure.[5]

It occurs as phenocrysts in alkalic volcanic rocks; in nodules of peridotite and gabbro in alkalic basalts; in syenites, monzonites and carbonatite tuffs. Mineral association includes titanian augite, rhoenite, olivine, ilmenite, spinel, plagioclase and titanian pargasite.[1]

It was first described in 1884 and is named for Qaersut (formerly Kaersut), Umanq district in northern Greenland.[2]