Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba)
Agates in Paleocene/Eocene tuffs from El Picado/Los Indios, Cuba were investigated to characterize the mineral composition of the agates and to provide data for the reconstruction of agate forming processes. The volcanic host rocks are strongly altered and fractured and contain numerous fissures and...
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MDPI AG
2021-05-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/11/5/531 |
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| author | Jens Götze Klaus Stanek Gerardo Orozco Moritz Liesegang Tanja Mohr-Westheide |
| author_facet | Jens Götze Klaus Stanek Gerardo Orozco Moritz Liesegang Tanja Mohr-Westheide |
| author_sort | Jens Götze |
| collection | DOAJ |
| description | Agates in Paleocene/Eocene tuffs from El Picado/Los Indios, Cuba were investigated to characterize the mineral composition of the agates and to provide data for the reconstruction of agate forming processes. The volcanic host rocks are strongly altered and fractured and contain numerous fissures and veins mineralized by quartz and chalcedony. These features indicate secondary alteration and silicification processes during tectonic activities that may have also resulted in the formation of massive agates. Local accumulation of manganese oxides/hydroxides, as well as uranium (uranyl-silicate complexes), in the agates confirm their contemporaneous supply with SiO<sub>2</sub> and the origin of the silica-bearing solutions from the alteration processes. The mineral composition of the agates is characterized by abnormal high bulk contents of opal-CT (>6 wt%) and moganite (>16 wt%) besides alpha-quartz. The presence of these elevated amounts of “immature” silica phases emphasize that agate formation runs through several structural states of SiO<sub>2</sub> with amorphous silica as the first solid phase. A remarkable feature of the agates is a heterogeneous distribution of moganite within the silica matrix revealed by micro-Raman mapping. The intensity ratio of the main symmetric stretching-bending vibrations (A<sub>1</sub> modes) of alpha-quartz at 465 cm<sup>−1</sup> and moganite at 502 cm<sup>−1</sup>, respectively, was used to depict the abundance of moganite in the silica matrix. The zoned distribution of moganite and variations in the microtexture and porosity of the agates indicate a multi-phase deposition of SiO<sub>2</sub> under varying physico-chemical conditions and a discontinuous silica supply. |
| first_indexed | 2024-03-10T11:19:18Z |
| format | Article |
| id | doaj.art-a7df8dbdccf749c8809d485f2805732e |
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| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-10T11:19:18Z |
| publishDate | 2021-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Minerals |
| spelling | doaj.art-a7df8dbdccf749c8809d485f2805732e2023-11-21T20:11:34ZengMDPI AGMinerals2075-163X2021-05-0111553110.3390/min11050531Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba)Jens Götze0Klaus Stanek1Gerardo Orozco2Moritz Liesegang3Tanja Mohr-Westheide4Institute for Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, 09599 Freiberg, GermanyInstitute for Geology, TU Bergakademie Freiberg, Cottastraße 4, 09599 Freiberg, GermanyDepartamento de Geología, Universidad de Moa, Avenida Calixto Garcia Iñiguez 15, Moa, Holguín 83330, CubaInstitute for Geological Sciences, FU Berlin, Malteserstraße 74–100, 12249 Berlin, GermanyInstitute for Evolution and Biodiversity Science, Museum für Naturkunde, Invalidenstraße 43, 10115 Berlin, GermanyAgates in Paleocene/Eocene tuffs from El Picado/Los Indios, Cuba were investigated to characterize the mineral composition of the agates and to provide data for the reconstruction of agate forming processes. The volcanic host rocks are strongly altered and fractured and contain numerous fissures and veins mineralized by quartz and chalcedony. These features indicate secondary alteration and silicification processes during tectonic activities that may have also resulted in the formation of massive agates. Local accumulation of manganese oxides/hydroxides, as well as uranium (uranyl-silicate complexes), in the agates confirm their contemporaneous supply with SiO<sub>2</sub> and the origin of the silica-bearing solutions from the alteration processes. The mineral composition of the agates is characterized by abnormal high bulk contents of opal-CT (>6 wt%) and moganite (>16 wt%) besides alpha-quartz. The presence of these elevated amounts of “immature” silica phases emphasize that agate formation runs through several structural states of SiO<sub>2</sub> with amorphous silica as the first solid phase. A remarkable feature of the agates is a heterogeneous distribution of moganite within the silica matrix revealed by micro-Raman mapping. The intensity ratio of the main symmetric stretching-bending vibrations (A<sub>1</sub> modes) of alpha-quartz at 465 cm<sup>−1</sup> and moganite at 502 cm<sup>−1</sup>, respectively, was used to depict the abundance of moganite in the silica matrix. The zoned distribution of moganite and variations in the microtexture and porosity of the agates indicate a multi-phase deposition of SiO<sub>2</sub> under varying physico-chemical conditions and a discontinuous silica supply.https://www.mdpi.com/2075-163X/11/5/531agatealpha-quartzchalcedonymoganiteopal-CTRaman spectroscopy |
| spellingShingle | Jens Götze Klaus Stanek Gerardo Orozco Moritz Liesegang Tanja Mohr-Westheide Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) Minerals agate alpha-quartz chalcedony moganite opal-CT Raman spectroscopy |
| title | Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) |
| title_full | Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) |
| title_fullStr | Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) |
| title_full_unstemmed | Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) |
| title_short | Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba) |
| title_sort | occurrence and distribution of moganite and opal ct in agates from paleocene eocene tuffs el picado cuba |
| topic | agate alpha-quartz chalcedony moganite opal-CT Raman spectroscopy |
| url | https://www.mdpi.com/2075-163X/11/5/531 |
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