Szakáll Sándor - Weiszburg Tamás szerk.: A telkibányai érces terület ásványai (Topographia Mineralogica Hungariae 2. Miskolc, 1994)

A telkibányai opálváltozatok ásványtani vizsgálata (Takács József)

Topographia Mineralogica Hungáriáé Vol. II. 209-223 Miskolc, 1994 A TELKIBÁNYAI OPÁLVÁLTOZATOK ÁSVÁNYTANI VIZSGÁLATA Mineralogical study of the opal varieties from Telkibánya, NE-Hungary Takács József Abstract Opal is a common but still poorly known silica mineral. Hungary and especially the Tokaj Mts., NE-Hungary is rich in opal varieties. Telkibánya is a famous locality for opal since the second half of the 18th century. Beside the best known yellow ("honey" or "wax") opal several more coloured varieties (greenish, reddish-yellow, yellowish-red, black and fire opal), milky opal and precious opal from Telkibánya were studied by applying a complex mineralogical approach (polarised light microscopy, X-ray powder diffraction (Fig. 2), TEM (Figures 1, 4, 5, 6), SEM (Fig. 7), SAED, EPMA, Mössbauer spectroscopy (Fig. 3), VIS spectrophotometry (Table I), DTA, TG, wet chemical analysis (Table II), high pressure experiments (Table III)). The results proved that the structure of opal should be characterized on two different levels, which are the microstructure (nm range, Fig. 1) and the secondary structure (pm range, Fig. 2,4, 5). All the Telkibánya opal varieties show opal-CT type microstructure and thus they can be well characterized by the recently introduced OR-index (Fig. 1). Both micro- (Fig. 1/c) and secondary (Fig. 4,5) structures of fire opal from Telkibánya are similar to those of fire opal from Mexico. The secondary structure of milky and precious opal varieties consists of spheres of 0.1-0.2 m. The size, the shape and the high symmetry of ordering of these morphological units cause an optical diffraction phenomenon similar to the Australian and different from the Cervenica, Slovakia precious varieties. The different colours of the coloured varieties are caused by O "Fe charge transfer. Water content and crystallinity of opal are independent. High pressure experiments show opal to be a stable phase in nature (Table III). OR-index can be used for characterization and comparison of genetics of opal-CT bearing formations of volcanic (hydrothermal) and sedimentary origin. Összefoglalás A szilícium-dioxid ásványok között az egyik sokat vizsgált, de ennek ellenére nem kielégítően ismert ásványfaj az opál. Magyarország és ezen belül a Tokaji-hegység kiemelkedően gazdag opálelőfordulásokban. A hegység legfigyelemreméltóbb lelőhelye Telkibánya, ahol a különböző színes változatok (zöldes, sárga, vörösessárga, sár-