Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a mineral which has historically been known to occur only in one locality - in Dolni Bory in Moravia. Until 1968 it was mistaken for cordierite. It was named after a Czech mineralogist, Josef Sekanina. Next to Brazilianite and Bukovskyite, Sekaninaite is probably the only other newly discovered mineral, which appears in fairly substansial quantities and therefore has great interest for collectors.
It appears in the form of imperfect, large crystals and in coarsely granular or compact aggregates of a violet or grey-blue colour, which tend to turn green or yellow through the effects of weathering. Like Cordierite, Sekaninaite too alters into different types of mica, chiefly into Muscovite. Some forms used to be described misleadingly as pinite (after the deposit of Cordierite pseudomorphs from the Pini mine near Schneeberg in Germany) or as Gigantolite (because it forms pseudomorphs after the gigantic crystals of Cordierite). Similar pseudomorphs occur in several localities in the Czech Republic, particularly near Jihlava and by Dylen in the Bohemian Forest. But they are altered to such a degree that it is impossible to determine whether Sekaninaite or Cordierite was the original material.
Pegmatite in contact with gneisses of sedimentary origin (paragneisses) are the parent rock of Sekaninaite. Sekaninaite has also recently been discovered in Japan.