Tracing the continental diagenetic loop of the opal-A to opal-CT transformation with X-ray diffraction

Liesegang, Moritz; Tomaschek, Frank

doi:10.1016/j.sedgeo.2020.105603

Cited by 21 publications

(20 citation statements)

References 48 publications

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“…In addition, columns have a smaller ξ value than matrix, which means that the degree of order of tridymite structural units increases from the matrix to the columns. At the bottom of the sample, a larger proportion of "tridymite" transforms into "cristobalite", tridymite nanoregions are better ordered in columns, and this state is closer to the end stage of opal-CT formation [12,25,48]. Therefore, we confirm that columns should represent an earlier stage of diagenetic alternation as compared with the matrix, which is consistent with the steps of digit formation [23].…”

Section: Differences Between Columns and Matrix In Microcrystalline Osupporting

confidence: 78%

Crystallinity and Play-of-Colour in Gem Opal with Digit Patterns from Wegel Tena, Ethiopia

Zhao

Bai

2020

Minerals

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A typical feature of Wegel Tena opal is the "digit pattern". This pattern consists of two parts, columns and matrix, with different colours, transparency or play-of-colour effect, which is still unexplained. This study aims at investigating the various parts of the digit pattern using different spectroscopic methods, and scanning and transmission electron microscopy (SEM and TEM). The band at 780 cm−1 on the Fourier transform infrared (FTIR) spectrum is correlated to the symmetric stretching vibration of Si–O. The bands at 1085, 895, 785 and 3600 cm−1 on Raman spectra indicate that Wegel Tena opal is opal-CT. Comparison of the relative intensity of the Raman signals around 360 cm−1 indicates that the microcrystalline opal on the top of the sample contains a higher amount of tridymite-like structural units, and the tridymite-type regions in the matrix contain a higher degree of structural defects. Silica spheres in the columns tend to be smaller and better ordered than in the matrix. The diameter of the silica spheres (d = 80–500 nm) or agglomerates (d = 200–580 nm) in Wegel Tena opal satisfies the conditions of diffraction of visible light, and the thickness of the silica layer (h = 120–200 nm) satisfies the conditions for film interference.

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Section: Differences Between Columns and Matrix In Microcrystalline Osupporting

confidence: 78%

Crystallinity and Play-of-Colour in Gem Opal with Digit Patterns from Wegel Tena, Ethiopia

Zhao

Bai

2020

Minerals

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“…A range of delay times spanning 0-400 s was employed. After some experimentation the delays used were 1, 2, 3,5,7,10,15,20,25,35,50,75,100,200 and 400 s in addition to the zero-time value. Longer delay times are impractical as the 400 s experiment delay time experiment required almost 20 h of collection alone.…”

Section: Methodsmentioning

confidence: 99%

“…Next, we examine potential trends across the opal-CT range which might result from the proposed transition (diagenesis) from of opal-A to quartz and moganite [12,[34][35][36][37][38][39][40]. In previous work [9] we showed correlations between features associated with the four constituent major peaks at 4.3, 4.1, 3.9 and 2.5 Å in the XRD patterns.…”

Section: Implications For Characterisation Of Opal-ctmentioning

confidence: 99%

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29Si Solid-State NMR Analysis of Opal-AG, Opal-AN and Opal-CT: Single Pulse Spectroscopy and Spin-Lattice T1 Relaxometry

et al. 2022

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Single pulse, solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy offers an additional method of characterisation of opal-A and opal-CT through spin-lattice (T1) relaxometry. Opal T1 relaxation is characterised by stretched exponential (Weibull) function represented by scale (speed of relaxation) and shape (form of the curve) parameters. Relaxation is at least an order of magnitude faster than for silica glass and quartz, with Q3 (silanol) usually faster than Q4 (fully substituted silicates). 95% relaxation (Q4) is achieved for some Australian seam opals after 50 s though other samples of opal-AG may take 4000 s, while some figures for opal-AN are over 10,000 s. Enhancement is probably mostly due to the presence of water/silanol though the presence of paramagnetic metal ions and molecular motion may also contribute. Shape factors for opal-AG (0.5) and opal-AN (0.7) are significantly different, consistent with varying water and silanol environments, possibly reflecting differences in formation conditions. Opal-CT samples show a trend of shape factors from 0.45 to 0.75 correlated to relaxation rate. Peak position, scale and shape parameter, and Q3 to Q4 ratios offer further differentiating feature to separate opal-AG and opal-AN from other forms of opaline silica. T1 relaxation measurement may have a role for provenance verification. In addition, definitively determined Q3 / Q4 ratios are in the range 0.1 to 0.4 for opal-AG but considerably lower for opal-AN and opal-CT.

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“…where λ is the wavelength of the X-ray, ө is the diffraction angle and ᵝ is the FWHM using different laser fluences (1.27, 1.59, 1.9) J/cm 2 . Films undergo strain and dislocation in their structure, and these parameters were calculated [12] as Equations ( 2) and (3), respectively [13]. The calculated values are given in TABLE 3a-c.…”

Section: Structural Characteristicsmentioning

confidence: 99%

Preparation of Nickel Oxide Microparticles by Pulsed Laser Ablation and Application to Gas Sensors

Hussain¹,

Abbas²,

Latif³

2021

ETJ

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Nickel oxide (NiO) microparticles were synthesized by pulsed laser ablation in double deionized water and intensively studied using Nd:YAG laser. The obtained sample was examined by X-ray diffraction, XRD measurement which tests the existence of polycrystalline. The structural parameters introduced and surface morphology was studied using field emission scanning electron microscopy devices. The optical properties of microparticles in a liquid were investigated through UV-VIS spectroscopy. The CO/CO2 sensing properties of the NiO microstructure sensors were systematically investigated, and the effects of different laser fluencies on the CO/CO2 sensing characteristics were analyzed. XRD measurements reflected the existence of polycrystalline, the optical result shows that The absorption spectra peak centered around 360 nm and a tail extending to the red region (600 nm), the scanning electron microscopy images showed that the morphologies of NiO thin films have microspheres in various. The sample affected by laser fluence 1.9 J/cm2 which exhibits the best sensitivity for CO2 gas.

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Tracing the continental diagenetic loop of the opal-A to opal-CT transformation with X-ray diffraction

Cited by 21 publications

References 48 publications

Crystallinity and Play-of-Colour in Gem Opal with Digit Patterns from Wegel Tena, Ethiopia

Crystallinity and Play-of-Colour in Gem Opal with Digit Patterns from Wegel Tena, Ethiopia

29Si Solid-State NMR Analysis of Opal-AG, Opal-AN and Opal-CT: Single Pulse Spectroscopy and Spin-Lattice T1 Relaxometry

Preparation of Nickel Oxide Microparticles by Pulsed Laser Ablation and Application to Gas Sensors

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