Kaersutite

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

Kaersutite
Kaersutite in tuff.jpg
General
CategoryInosilicate
Formula
(repeating unit)
NaCa2(Mg3Ti4+Al)(Si6Al2)O22(OH)2
Strunz classification9.DE.10
Dana classification66.01.03a.18
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Identification
ColorDark brown to black - yellow-brown, green-brown, or red-brown in thin section
Crystal habitPrismatic phenocrysts, granular aggregates
TwinningSimple or multiple twinning parallel to {100}
CleavagePerfect on {110}, intersecting at 56° and 124°
TenacityBrittle
Mohs scale hardness5 - 6
LusterVitreous
StreakPale brownish-grey
DiaphaneitySemitransparent
Specific gravity3.20 - 3.28
Optical propertiesBiaxial (-)
Refractive indexnα = 1.670 - 1.689 nβ = 1.690 - 1.741 nγ = 1.700 - 1.772
Birefringenceδ = 0.030 - 0.083
PleochroismStrong; X = yellow, yellow-brown; Y = red, red-brown; Z = deep brown, dark red-brown.
2V angle66 - 82°
References[1][2][3][4]

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]

ReferencesEdit