Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 92. (Budapest 2000)

Embey-Isztin, A. ; Scharbert, H. G.: Glasses in peridotite xenoliths from the western Pannonian Basin

tain a few large relict spinel grains. They are texturally controlled, following the former places of clinopyroxene and spinel and they are delineated by former grain boundaries, however occasionally they also form embayments into olivine and orthopyroxene. Szt1034 also contains similar blebs (Fig. 1), however in this rock glass is more conspicuous in interstitial areas forming narrow veins (Figs 3, 5). A few of these veins contain small needles of quench plagioclase and some carbonates, however most of the veins of glass are devoid of such crystals. We found that glass formation is more frequent in poikilitic xenoliths than in xenoliths with other texture types, in fact the majority of our glass-bearing samples belong to this special group (Szt1006, Szt-1033, Szt1034, Szt-1

106 and Szt-1

116). In general, clinopyroxenes in peridotites of this textural group seem to be unstable and almost always show variable degrees of decomposition ranging from a thin spongy rim around the crystals to complete disintegration of the original grains. Figs 1-4. 1 : Disintegrated large primary clinopyroxene grain in sample Szt1034, containing secondary small clinopyroxene and spinel crystals, vugs and glass. II N, M=20x. 2: Small patch of lilac brown interstitial glass, G-1055, II N, M=20x. 3: Narrow vein-system filled by glass, quench plagioclase and vugs, Szt-1

034, + N, M=20x. 4: Disintegrated primary clinopyroxene grains in Szt-1033, II N, M=20x.