kaersutite

{{Infobox mineral | name = Kaersutite | category = Inosilicate | boxwidth = | boxbgcolor = | image = Kaersutite in tuff.jpg | imagesize = | alt = | caption = Kaersutite (black) in tuff. Locality: Suletice, Czech Republic | formula = NaCa2(Mg3Ti4+Al)(Si6Al2)O22(O)2 | IMAsymbol = Krs | molweight = | strunz = 9.DE.10 | dana = 66.01.03a.18 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/m | color = Dark brown to black, yellow-brown, green-brown, or red-brown in thin section | colour = | habit = Prismatic phenocrysts, granular aggregates | twinning = Simple or multiple twinning parallel to {100} | cleavage = Perfect on {110}, intersecting at 56° and 124° | fracture = | tenacity = Brittle | mohs = 5–6 | luster = Vitreous | streak = Pale brownish-grey | diaphaneity = Semitransparent | gravity = 3.20–3.28 | density = | polish = | opticalprop = Biaxial (−) | refractive = 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 = 66–82° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Kaersutite is a dark brown to black double-chain calcic titanium-bearing amphibole mineral with formula: NaCa2(Mg3Ti4+Al)(Si6Al2)O22(O)2.

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