The origin of opal-bearing listvenite from the Tokat Region (northern Turkey)
  
Yazarlar (5)
Doç. Dr. Zeynel BAŞIBÜYÜK Kırşehir Ahi Evran Üniversitesi, Türkiye
Tomasz Powolny
Uniwersytet Jagielloński, Polonya
Dr. Öğr. Üyesi İlkay KAYDU AKBUDAK Kırşehir Ahi Evran Üniversitesi, Türkiye
Magdalena Dumańska-Słowi̇K
Agh University Of Krakow, Polonya
Doç. Dr. Gökhan EKİNCİOĞLU Kırşehir Ahi Evran Üniversitesi, Türkiye
Makale Türü Açık Erişim Özgün Makale (SSCI, AHCI, SCI, SCI-Exp dergilerinde yayınlanan tam makale)
Dergi Adı Mineralogical Magazine (Q3)
Dergi ISSN 0026-461X Wos Dergi Scopus Dergi
Makale Dili İngilizce Basım Tarihi 01-2025
Cilt / Sayı / Sayfa 0 / 1 / – DOI 10.1180/mgm.2025.10174
Makale Linki https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7D883F1D995B7D9ED223E0D3DF85C19E/S0026461X25101746a.pdf/div-class-title-the-origin-of-opal-bearing-listvenite-from-the-tokat-region-northern-turkey-div.pdf
Özet
The following study reveals the mineralogy and origin of peculiar silica-carbonate bodies (i.e. listvenite) associated with tectonized serpentinites and Permian–Triassic phyllites from the Tokat region in northern Turkey. The listvenite includes green-coloured opaline silica intersected by saddle dolomite and minor sulphide mineralization (pyrite, cobaltite, and enargite). It also hosts abundant chalcedonic bodies (i.e. vein agate) of bluish to bluish-white colouration. Listvenite-hosted opaline silica has been recognized as lussatite (i.e. a fibrous birefringent opal-CT variety) with a dominantly ,,tridymitic” structure, whilst its green colouration results from discrete, but widely disseminated Cr-bearing smectite-group minerals, such as volkonskoite and/or Cr-montmorillonite. Chromium, the main colouring agent determined by elemental mapping and visible-light spectroscopy, was likely sourced from spinel-group minerals (e.g. chromite) whose relics mark the presence of the ultramafic protolith. In contrast, the vein agate is composed of length-fast chalcedony, with subordinate quartzine and minor opaline silica, followed by drusy quartz. Its bluish colour appears to be related to scattering effects enhanced by elevated moganite content (up to 46 wt.%). The observed mineral paragenesis suggests at least a two-stage evolution: (1) early listvenitization marked by carbonate-silica alteration of the host serpentinite along with concomitant sulphide precipitation, and (2) subsequent silicification producing chalcedony (agate) veins under low- temperature conditions, followed by possible dissolution of the earlier saddle dolomite. This evolution reflects complex fluid-rock interactions involving CO2-rich, Ca-bearing, and later Si-rich fluids under fluctuating redox and pH conditions. Hence, the proposed crystallization sequence of the associated mineral assemblage is: sulphides (cobaltite+pyrite+enargite) → saddle dolomite → opal (lussatite) + Cr-smectite → chalcedony (agate). The findings provide new insights into the genesis, colouration mechanisms, and structural state of Cr-bearing opaline and chalcedonic silica in altered ultramafic terrains.
Anahtar Kelimeler
agate | chalcedony | chrome opal | listvenite | lussatite | saddle dolomite