Abstract

Gehlenite is a common mineral in three high-temperature calcic skarns in Romania: Măgureaua Vaţei and Cornet Hill in Apuseni Mountains and Oraviţa in Banat. In all three occurrences, a gehlenite zone occurs within the contact between dioritic or monzodioritic bodies of Upper Cretaceous age and carbonaceous sequences of Mesozoic age. The melilite solid-solutions vary from Ak34.1 to Ak51.2 (mean Ak41.2) at Oraviţa, from Ak30.4 to Ak42.9 (mean Ak38.3) at Măgureaua Vaţei, and from Ak24.3 to Ak41.7 (mean Ak32.9) at Cornet Hill, respectively. The content of “Na-melilite” is low, from up to 1.96 mol.% at Cornet Hill to up to 3.60 mol.% at Oraviţa. The cell parameter a ranges from 7.679(3) to 7.734(3) Å at Oraviţa, from 7.683(4) to 7.735(1) Å at Măgureaua Vaţei, and from 7.684(3) to 7.733(1) Å at Cornet Hill, whereas c varies from 5.043(3) to 5.065(3) Å at Oraviţa, from 5.040(1) to 5.070(3) Å at Măgureaua Vaţei, and from 5.044(1) to 5.067(4) Å at Cornet Hill. It is not possible to quantify the variations in the crystallographic parameters by considering only the åkermanitic substitution because the “Na-melilite” and “Fe-åkermanite” substitutions also play an important role. The cell parameter a remains practically constant within experimental errors, in spite of the increasing åkermanite-for-gehlenite substitution, due to the opposite influence of the “Na-melilite” component. The åkermanite substitution prevails over the opposite influence of “Na-melilite” in increasing the cell volume, and is additive to the influence of “Na-melilite” in decreasing the cell parameter c. The record in the infrared-absorption spectra of bands located at ~855 cm−1 and ~670 cm−1, respectively, which may be tentatively assigned to Al–O–Al stretching, is indicative of the presence of gehlenite-rich members of the melilite group in all the three occurrences.

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