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Journal Article
Journal: Geology
Published: 03 January 2023
Geology (2023) 51 (2): 189–192.
... of crystal growth within the gel. Over time, the gel hardened to form opal-A G . This silica phase is thermodynamically unstable and recrystallized to quartz that has a distinct mosaic texture. The opaline veins at the McLaughlin deposit are composed primarily of relict silica microspheres, which...
Journal Article
Journal: Geology
Published: 02 December 2022
Geology (2023) 51 (1): 85–90.
... increase in acoustic impedance; Figs. 1B and 2C ). X-ray diffraction measurements from ODP Site 762 also show that sediments above H1 have high concentrations of opal-A, whereas below H1, the sediment has high concentrations of opal-CT ( Fig. 1B ). H1 therefore corresponds to the opal-A to opal-CT...
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Series: GSA Special Papers
Published: 26 September 2022
DOI: 10.1130/2022.2556(04)
EISBN: 9780813795560
... ABSTRACT The Monterey Formation and related formations in California have long been the subject of field and laboratory studies on silica diagenesis. Biogenic or amorphous silica (opal-A) alters to a more-ordered opal-CT and eventually to the crystalline end member, quartz, with increasing...
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Journal Article
Journal: Lithosphere
Publisher: GSW
Published: 16 August 2022
Lithosphere (2022) 2022 (Special 9): 8587468.
... and the biogenic content. Based on six VPCA components of first derivative reflectance spectrum measurements and laboratory analyzed biogenic contents of core MD972148, a set of empirical equations for estimating CaCO 3 , TOC, and opal contents have been established. The equations were tested using data from core...
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Journal Article
Published: 01 July 2022
American Mineralogist (2022) 107 (7): 1353–1360.
...Seungyeol Lee; Huifang Xu; Hongwu Xu Abstract The structure of opal-A was not fully understood due to its poorly crystalline nature. To better understand its structural characteristics, we have analyzed opal-AN (amorphous-network) and opal-AG (amorphous-gel) using synchrotron X-ray diffraction (XRD...
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Journal Article
Journal: GSA Bulletin
Published: 11 May 2021
GSA Bulletin (2022) 134 (1-2): 348–370.
... level of RSS3-Ia (from <1700 m/s to >2500 m/s; Supplemental Fig. S3). The outstanding character of RSS3-Ia is related to the silica cemented mudstones and chert revealed in the lithology, and the above average Si/Ti ratios in cores recovered at Site U1521 ( McKay et al., 2019 ). The opal content...
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