Needles of ferro-gedrite on cleavage plane (001) of sekaninaite. Ferrogedrite is a product of weathering and decay of sekaninaite. From: Dolní Bory, Křižanov, Žďár nad Sázavou, Vysočina Region, Czech Republic. — Photo: David Hospital · CC BY-SA 4.0
Sekaninaite
The iron analogue of cordierite — described in 1968 from Dolní Bory, Moravia.
Intro adapted from Wikipedia (CC BY-SA).
Sekaninaite is an IMA-recognized mineral species in the silicate class, with the chemical formula Fe²⁺₂Al₄Si₅O₁₈.
It crystallizes in the orthorhombic crystal system (space group Cccm). It is a member of the Beryl structural group.
Key properties: Mohs hardness 7–7.5; specific gravity 2.76–2.77; Vitreous luster; refractive index 1.57; optically biaxial.
IMA symbol Skn, IMA status: approved, named in 1967.
Found in the albite zone of pegmatites in granulites and gneisses (Doln¶³ Bory, Czech Republic); in bauxitic lithomarge intensely altered by a diabase plug (Brockley, Ireland).
It is found associated with Albite, quartz (Doln¶³ Bory, Czech Republic).
The name refers to Professor Josef Sekanina (1901{), Czech mineralogist who first discovered the mineral.