A mineral which was known from the past to occur only in one locality- in Doini Bory
. Until 1968 it was taken for cordierite
. Only a short while ago it was named after a Czech
mineralogist, Josef Sekanina
. Next to brazilianite
, sekaninaite is probably the only other newly discovered mineral, which appears in fairly substantial occurrences 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 of 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.