Powolny Tomasz, Dumańska-Słowik Magdalena, Szczerbowska-Boruchowska Magdalena, Woszczyna Maciej
Faculty of Natural Sciences - Institute of Earth Sciences, University of Silesia in Katowice, 60 Będzińska St, Sosnowiec, 41-200, Poland.
Faculty of Geology, Geophysics, and Environmental Protection, AGH University of Krakow, 30 Mickiewicza Ave, Krakow, 30-059, Poland.
Sci Rep. 2024 Sep 28;14(1):22473. doi: 10.1038/s41598-024-73136-x.
Basalt-hosted monocentric agates from Bou Hamza (Morocco) were examined to unravel a discrete relationship between moganite content, water content, and the abundance of various types of chalcedony/quartz microtextures, so that the agate-forming process is refined. Herein, moganite content is noticeably low in length-slow chalcedony (quartzine, up to 18 wt.%), as compared with the co-occurring length-fast (LF) chalcedony (up to 31 wt.%). Such a type of disparity reflects a stabilization of the crystallization front during the formation of chalcedonic bands. Recrystallization-related quartz types (i.e. feathery and mosaic/jigsaw puzzle) show low and high moganite content (0 and up to 34 wt.%, respectively) since they have likely originated from different silica precursors (i.e. opaline and chalcedonic, respectively). Meanwhile, the initial formation of mosaic quartz can be exclusively witnessed in the so-called zebraic variety of length-fast chalcedony (i.e. with twisted fibres) that should be hence regarded as a ,,metastable" variety of silica though. The range of total water content remains quite stable across chalcedonic bands (0.5-0.6 wt%) and reaches the highest values (0.7 wt%) in feathery quartz. However, there is rather a general negative relationship between the content of molecular water and silanol-group water. This can stem from the recycling of water species following the condensation reaction of silanols within the agate geodes. The agates originated from Fe-Ti-bearing solutions that co-precipitated goethite, hematite, and rutile, but also contain minor low-grade carbonaceous material.
对来自布哈扎（摩洛哥）的玄武岩中 hosted 的单中心玛瑙进行了研究，以揭示莫来石含量、水含量与各种类型玉髓/石英微观结构丰度之间的离散关系，从而完善玛瑙形成过程。在此，与共生的长度快（LF）玉髓（高达 31 wt.%）相比，长度慢的玉髓（石英质，高达 18 wt.%）中的莫来石含量明显较低。这种差异反映了玉髓带形成过程中结晶前沿的稳定。与重结晶相关的石英类型（即羽毛状和镶嵌/拼图状）显示出低和高的莫来石含量（分别为 0 和高达 34 wt.%），因为它们可能分别源自不同的二氧化硅前驱体（即蛋白石和玉髓）。同时，镶嵌石英的初始形成仅在所谓的长度快的玉髓的斑马纹变种（即具有扭曲纤维）中可见，不过这种变种应被视为二氧化硅的“亚稳”变种。整个玉髓带的总水含量范围相当稳定（0.5 - 0.6 wt%），在羽毛状石英中达到最高值（0.7 wt%）。然而，分子水和硅醇基水的含量之间通常存在负相关关系。这可能源于玛瑙晶洞中硅醇缩合反应后水物种的循环利用。这些玛瑙源自含铁钛的溶液，该溶液同时沉淀了针铁矿、赤铁矿和金红石，但也含有少量低品位碳质材料。
