Problem rozpoznawania paramorfoz kwarcu niskotemperaturowego po wysokotemperaturowym

Abstract

ON DISCERNING OF LOW- AFTER HIGH-QUARTZ PARAMORPHS Summary The criteria of high → low quartz inversion are discussed in the present paper. On the basis of material collected by the author, the criterion of habit as well as fractures and other morphological criteria are verified. The reinvestigation of morphology of Dauphiné twins as the criterion of inversion (Barsanov's and Gureva's method, cf. 1, 2 & 7) on the 60 specimens was made and there was ascertained, that the method gave positive results for the majority of investigated specimens. As the supplementary method, the Dennen's (3) aluminium thermometry for quartz (55% of positive results) was used for the selection of specimens; determination of crystallization temperatures by the fluid inclusion methods was the main thermometric method used in the recent investigation. Specimens (over 100), selected as above, were investigated by the m absorption method in the 3 μm region as described in the papers of Dolomanova & al. (4, 5). Dolomanova & al. suggested. That the absorption band of molecular H2O (3400-3500 cm-1) can be used as the criterion of primary higher low-quartz crystallization. The low intensity of the band would be characteristic for paramorphs after high quartz, and the primary low quartz ought to give the absorption band of high intensity. Author's investigations permitted to ascertain, that the absorption intensity of band of molecular H2O (mainly entrapped in fluid inclusions) depends on: 1) size and amount of inclusions; 2) amount of water in inclusion filling. Molecular H2O can present both in primary and in secondary inclusions, and the secondary ones are usually more numerous than primary. On the other hand, high quartz bears minor amount of rather poor in water primary inclusions and various but usually higher amounts of secondary, rich in water inclusions; the latter will determine the intensity of the named absorption band. There also exists a number of low quartzes bearing only individual aqueous inclusions and without the band of molecular H2O in their spectrum. As the amount of water in quartz does not depend immediately on the phase inversion, the intensity of m absorption band of molecular water cannot be the criterion of presence of low- after high-quartz paramorphs.