Szakáll Sándor - Fehér Béla: A polgárdi Szár-hegy ásványai (Topographia Mineralogica Hungariae 8. Miskolc, 2003)
Kalcium-szilikátok a polgárdi Szár-hegy wollastonitos szkarnjából (Fehér Béla és Sajó István)
Topographia Mineralogica Hungáriáé Vol. VIII. 87-113. Miskolc, 2003 Kalcium-szilikátok a polgárdi Szár-hegy wollastonitos szkarnjából Calcium silicates from the wollastonite skarn of the Szár Hill, Polgárdi, Hungary FEHÉR Béla 1 * és SAJÓ István 2 1 Herman Ottó Múzeum, Ásványtár, 3525 Miskolc, Kossuth u. 13. 2 Magyar Tudományos Akadémia, Kémiai Kutatóközpont, 1025 Budapest, Pusztaszeri út 59-67. * E-mail: feherbela@axelero.hu Abstract The Devonian Polgárdi limestone is cross-cutted by Permian (?) rhyolite and Triassic (?) andésite dykes. Considerable skarn mineralization developed along the contacts between limestone and andésite dykes in two sharply separated zones: 1) diopside-vesuvianite zone near the andésite dykes and 2) wollastonite zone towards the limestone. This paper gives data about mineralogy and genesis of the rock-forming mineral (wollastonite) of the latter zone as well as its low temperature calcium silicates (apophyllite, thaumasite, okenite, nekoite and an unknown hydrous Ca silicate). Wollastonite forms granular (Fig. 3) or radial (Fig. 7) aggregates consisting of short prismatic (Fig. 4) and tabular, lath shaped crystals (Fig. 5) elongated on [010] up to 2 mm in length. Chemical formula of wollastonite is (Cao.89Mg 005 Feo. 0 |Alo.oi)z=o.96Sii.o2 03 according to the wet chemical analysis given in Table I. X-ray powder diffraction data are shown in Table II. In the wollastonite skarn the most abundant low temperature calcium silicate is apophyllite. It forms colorless, short columnar or pseudocubic crystals forming crusts on the fissures of the wollastonite skarn. Observed forms are {001}, {100} and {111} (Fig. 9). Apophyllite has white streak, pearly luster on {001} and vitreous luster on the other faces. Its chemical composition (Table IV, column 1): (Ko.99Nao.o[)r=i.ooCa 3 . 9 4Si 8 . 03 02o[(OH)o.96Fo.o4]s=i.oo • 8.90H 2 O, which corresponds to the hydroxyapophyllite species close to the ideal endmember composition. Its X-ray powder diffraction data are given in Table V. Thaumasite forms colorless, simple hexagonal columnar crystals up to 2 mm in length (Fig. 11) or white, tangled aggregates consisting of minute acicular crystals. Its X-ray powder diffraction data are shown in Table VI. Okenite is white with pearly or silky luster. It forms typical "cotton ball" like aggregates (Figs. 12, 13), the size of which are usually about 1 mm, but rarely can reach 3 mm in diameter. Okenite crusts are rather common on minerals developed earlier (calcite, apophyllite). Its chemical composition (Table IV, column 3): (Ca4 98 Nao. 0 iKo.oi)i=5.oo Si 9 .oo 0 2 3 • 10.14H 2 O. X-ray powder diffraction data are given in Table VII. Nekoite appears as colorless, acicular, 1-2 mm sized crystals which can rarely reach 1 cm in length. Crystals are arranged into radial groups with silky luster (Fig. 15). Its chemical composition (Table IV, column 5): (Ca 3 i 6 Fe 0 .oi)E=3.i7 Si 592 0 15 • 7.13H 2 0. X-ray powder diffraction data are shown in Table VIII. In the wollastonite skarn the most interesting mineral is an unknown, hydrous calcium silicate (SzH2 sample). In its chemical composition the Ca : Si ratio is equal to 6:1. SzH sample forms globular aggregates up to 2 mm in diameter consisting of minute acicular crystals (Fig. 16).
