Kónya Péter (szerk.): A Bakony-Balaton-felvidék vulkáni terület ásványai - TQS Monographs 1. (Miskolc - Budapest, 2015)

Kónya P. et al.: A Bakony-Balaton-felvidék vulkáni terület üregkitöltő zeolitjai

Kónya P. (szerk.) (2015): A Bakony-Balaton-felvidék vulkáni terület ásványai.

TQS Monographs 1. Miskolc-Budapest: Herman Ottó Múzeum és Magyar Földtani és Geofizikai Intézet, pp. 181-222.

A Bakony-Balaton-felvidék vulkáni terület üregkitöltő zeolitjai

Cavity filling zeolites from the Bakony-Balaton Highland Volcanic Field, Hungary

Kónya Péter1, Szakáll Sándor2, Simona Bigi3, Kovács-Pálffy Péter4, Földvári Mária5, Kákay Szabó Orsolya6

'Magyar Földtani és Geofizikai Intézet, 1143 Budapest, Stefánia út 14., e-mail: konya.peter@mfgi.hu 2Miskolci Egyetem, Ásvány- és Kőzettani Tanszék, 3515 Miskolc-Egyetemváros ’University of Modena and Reggio-Emilia, Department of Chemical and Geological Sciences, Modena, Italy

42518 Leányvár, Bécsi út 62.

51036 Budapest, Nagyszombat u. 4.

61021 Budapest, Tárogató u. 106.

Abstract

Zeolites are the most often cavity filling minerals in alkaline basalt of the Bakony-Balaton Highland Volcanic Field (BBHVF). Its mineral assemblage forms by hydrothermal fluids in the cooling volcanic flows. Zeolites have been well known for a long time at the BBHVF.

The paragenesis contains analcime, chabazite, garronite, gismondine, gmelinite, gobbinsite, leucite, natrolite group zeolites, offretite and phillipsite. These zeolites occur closely associated with calcite, smectite and other hydrothermal and supergene minerals.

Analcime occurs often as colourless, transparent crystals up to 0.5 mm on the miarolitic minerals or it forms bigger crystals (0.5 cm) on okenite. The dominant forms are {211} combined with {100}. The chemical analyses of analcime show that very small concentration of Ca is build in the structure indicating a Na/(Na+Ca) ratio of 0.94-0.99. Si/Al ratio ranges from 1.99 to 2.09, R (=Si/(Si+Al)) ranges from 0.67 to 0.68.

Chabazite appears as glassy, colourless pseudocubic rhombohedral {1011} crystals with diameters of 1-5 mm. More rarely it occurs as colourless phacolitic crystals or aggregates that are usually interpenetrating, forming lens- or star-shaped discoidal twins. WDS analyses show that Ca, Na and К occur as dominant cations in chabazite. Most crystals are chabazite- Ca. Chabazite-K and chabazite-Na were first identified from Hungary. Chabazite-Mg has been approved by IMA as new zeolite species of the chabazite series (IMA 2009-060). In some cases chabazite straddles chabazite-Ca to chabazite-K and it occurs as zoned crystals. Si/Al ratio ranges from 1.65 to 2.90, R ranges from 0.63 to 0.69.

Garronite is a very rare zeolite in BBHVF. It occurs as white, compact, radial aggregates (up to 2 mm) on the wall of cavities with phillipsite, smectite, calcite and chabazite. According to the chemical analyses the dominant extraframework cation of garronite is Ca with substantial Na and K. R is 0.62.

Gismondine appears as colourless, transparent crystals with dipyramid {232} faces on phillipsite in the basalt of Hajagos Hill. According to the XRD it is associated with phillipsite and garronite (Haláp Hill), chabazite (Tóti Hill), analcime, gonnardite-Na, natrolite and phillipsite (Uzsa quarry). Ca is the dominant extraframework cation, Na and К are present in very subordinate amounts. Si/Al ratio ranges from 1.12 to 1.18, R ranges from 0.53 to 0.54.

Gmelinite is a rare zeolite in the basalt of the BBHVF. Its colourless to white crystals (up to 1-2 mm) were found in cavities. Dominant forms are hexagonal dipyramid {1011} and prism faces {1010}. Si/Al ratio ranges from 2.07 to 3.48, R = 0.67-0.78. Na/(Na+Ca) ratio ranges from 0.08 (almost Na-free) to 0.71 (Na-rich).

Gobbinsite occurs as white, lustreless globular aggregates up to 1-3 mm. It was earlier identified in close association with okenite by XRD. In new samples it was found with phillipsite.

Leucite appears as reddish or black greyish unshapely grains up to 7 mm in close association with analcime and miarolitic minerals. Great amounts of leucite were found in Badacsonytördemic basalt quarry. It shows a small range of Si/Al (2.02-2.11) and of R (0.67-0.68), has К as dominant extraframework cation, and has low Ca and Mg content.

Natrolite group minerals include the following zeolites: natrolite, mesolite, scolecite, gonnardite-Na, paranatrolite and thomsonite-Ca. “Tetranatrolite” was discredited. The natrolite subgroup (natrolite to paranatrolite) occurs as colourless to white, transparent or translucent gappy or compact coating up to 3 mm on the wall of cavities. They appear often as radial aggregates or hemispheres up to 1 -1.5 cm. Thomsonite-Ca occurs as colourless to white crystals up to 1 -4 mm of size in radial aggregates. The chemical composition of natrolite and paranatrolite are close to the schematic formula. Mesolite has little higher contents of Ca and scolecite and thomsonite-Ca contain important amounts of Na. The chemical composition of gonnardite-Na is highly variable. Na/(Na+Ca) ratio ranges from 0.65 to 0.97.

Offretite was described first from Prága Hill, Bazsi. Recently it was identified from Sarvaly Hill, Sümeg. It occurs as colourless, transparent crystals 20-30 pm in width and 100 pm in length. Offretite rarely appears as radial aggregates. This zeolite is found in close association with calcite and smectite (saponite). Si/Al ratio ranges from 2.67 to 2.70, R is 0.73. Ca and Mg are the dominant extraframework cations, К and Na occur in very low amounts.

Phillipsite is the most common zeolite in basalt of the BBHVF. It has three types of twins as Marburg, Perier and Stempel twin. Marburg twin of these is the most frequent in cavities. It is composed of prism faces are (010) and (110)