O seladonicie z Barczy w Górach Świętokrzyskich

Abstract

CELADONITE FROM BARCZA IN THE ŚWIĘTY KRZYŻ MOUNTAINS

Celadonite occurs as chief component of Lower Devonian (Emsian) tuffite appearing within the sandstones of the Barcza beds. lt forms 70 to 90% of the tuffite mass, occurring in the shape of submicroscopic plates the largest of which attains 0.02 mm. in their direction of elongation. Less frequently has celadonite been reported, in the shape. of spherulites, of 0.08-0.45 mm. diameter (Plate 1, Figs. 3, 4). Pleochroism of individual plates is almost unnoticeable, but aggregated deposits show in the N_γ direction a yellowish-green colour, whereas in the remaining directions they are yellowish or colourless. The investigated celadonite is uniaxial, or discloses an angle of optical axes 2V_α = 5°; it is optically negative. Measured in immersion fluid, the refractive index in direction N_γ is in some prisms = 1.579, in others = 1.581.