FOV ~ 4 x 6 mm. Found August 1999. MOB coll. According to Horváth et al (Min Rec 1990), kaersutite “is readily identifiable by its perfect prismatic cleavage and red internal reflections”. This photo attempts to show the perferct cleavage. At the top you can see that there are actually two perfect cleavages at an “amphibole angle". The fracture “perpendicular” to these is conchoidal and very glassy. Note: Per László (private comminication March 2017), all analyzed "kaersutite" is actually the new species ferri-kaersutite (IMA2014-051). The sample also displays the red highliughts but they hardly show up at this angle of illumination. See http://www.mindat.org/photo-173584.html for more than you may want to know about kaersutite at MSH and a pointer to a more general discussion about the mineral. Apart from the kaersutite – which altogether spans about 2½ x 2½ cm – this specimen is of interest because of the presence of "ilmenohematite" (~ 90% hematite) and apatite, neither of which appears on the MSH "list" for this environment (Lapis 2000) — Photo: Modris Baum · CC0
Ferri-kaersutite
The ferric-iron-dominant relative of kaersutite — a dark titanium-bearing calcic amphibole.
Intro adapted from Wikipedia (CC BY-SA).
Ferri-kaersutite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaCa₂(Mg₃Fe³⁺Ti)(Si₆Al₂)O₂₂O₂.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Amphibole-amphiboles sodic-calcic structural group.
Key properties: specific gravity 3.19; Vitreous luster.
IMA symbol Fkrs, IMA status: approved, named in 2014.
Found in an ultramafic (spinel-bearing lherzolite) mantle xenolith in alkaline mafic rock.
It is found associated with Forsterite, diopside, Cr-bearing spinel.
The name refers to an amphibole with sodium and calcium dominant in the A and B sites respectively, ferric iron in the C site and O2- dominant in the W site.