sekaninaite

{{Infobox mineral | name = Sekaninaite | category = Cyclosilicate | boxwidth = | image = File:Sekaninaite (cordierite) (Fe2+,Mg)2Al4Si5O18 (25837507710).jpg | alt = | caption = Sekaninaite from Dolní Bory, Czech Republic | formula = (Fe+2,Mg)2Al4Si5O18 | IMAsymbol = Skn | molweight = | strunz = 9.CJ.10 | dana = 61.02.01.02 Cordierite group | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: () | symmetry = Cccm | unit cell = a = 17.18 Å, b = 9.82 Å c = 9.29 Å; Z = 4 | color = Blue to blue-violet | colour = | habit = As poorly developed crystals | twinning = Commonly twinned on {110} and {310} | cleavage = {100}, imperfect; parting on {001} | fracture = | tenacity = | mohs = 7 – 7.5 | luster = Vitreous | streak = | diaphaneity = Transparent to translucent | gravity = 2.76 – 2.77 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.561 nβ = 1.572 nγ = 1.576 | birefringence = δ = 0.015 | pleochroism = | 2V = Measured: 66°, Calculated: 60° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a silicate mineral, the iron-rich analogue of cordierite.

It was first described in 1968 for an occurrence in Dolní Bory, Vysočina Region, Moravia, Czech Republic, and is now known also from Ireland, Japan, and Sweden. It was named after a Czech mineralogist, Josef Sekanina (1901–1986). In Brockley on Rathlin Island, Ireland sekaninaite occurs in bauxitic clay within the contact aureole of a diabase intrusive plug.