Apophyllite from the Mi dzyrzecze sillnear Bielsko-Bia a, the type of area of the teschenite-picrite association

Fluorapophyllite crystals from complex veins crosscutting a small pectolite skarn bodyat the top of the Miêdzyrzecze sill were studied by means of chemical analysis, X-ray diffraction, thermalanalysis and both infrared and Raman spectroscopy. The apophyllite from Miêdzyrzecze, lacking abnormaloptical properties, is tetragonal with lattice parameters: a = 8.974(2) , c = 15.798(6) . DTA curves exhibittwo endothermic peaks centred at about 330 and 430C. The dehydration behaviour of apophyllite resultsfrom the development on the outer parts of grains of an amorphous layer. It forms a diffusion barrier thatmoderates H2O migration and originates in the second endothermic peak. IR investigations showed a newstretching vibration (OH), not previously recognized in apophyllite. This new band at 3627 cm–1 can beattributed to (OH) of the hydroxyl group which substitutes for F– in the apophyllite structure. Selectiveleaching of phlogopite probably released the elements necessary for apophyllite precipitation in open spacesof the fissures in the upper part of the picrite sill.