Geology topics

Thomas Lameris

Publications and source records attributed to Thomas Lameris.

3 recordsLinked to original sources

USGS2024

Correlating quantified cathodoluminescence spectra in jadeite with micro-scale color measurements in visible-near infrared reflectance spectrometry

Cultures throughout history have valued jadeite jade (hereinafter jade), a natural material assemblage composed predominately of the NaAl endmember pyroxene, jadeite (NaAlSi 2 O 6 ) that is prized for its mechanical properties and enticing coloration [ 1 , 2 ]. The geological setting for the formation of jadeite-rich rocks and associated complex geochemical phenomena is well documented in the literature [ 3-5 ]. Unlike single crystal gems, jade often contains a mixture of colors, but the stone is perhaps best known for exhibiting a range of green hues from pale green to blue green, and to deep green [ 1 , 6 ]. Efforts to classify jade color include qualitative matching to a set of reference color tiles, and less commonly, use of a more quantitative set of color perception values first established by International Commission on Illumination’s (CIE 1931) color space, which includes values for light-dark luminance level (L*), a green-red vector (a*), and a blue-yellow vector (b*) [ 7 , 8 ]. Two principal mechanisms have been identified as the cause of green coloration in jadeite: 1) the chemical state of impurity Fe, either 2+ or 3+, and 2) minor to trace Cr in the crystal structure [ 9 , 10 ]. Previous studies have associated Cr 3+ with cathodoluminescence (CL) spectral features in jadeite using point spectrometry, with more recent connections made via 2D CL spectrum imaging [ 11-13 ]. In this effort, we are seeking to establish whether Cr impurities are correlated with green coloration in jadeite using micro-scale (≤110 μm) visible-near infrared (VIS-NIR) reflectance spectrometry.

Microscopy and Microanalysis↗

USGS2024

Cathodoluminescence imaging and spectrometry of a jadeite microbeam reference crystal: Detection of Ce3+

Options for selecting a high Na concentration mineral for instrument calibration that are suitably stable under the electron beam are limited [ 1 ]. NaCl (approximately a mass fraction of 39 % Na) is not practical for use alongside other embedded and polished materials in a mounted block of standards. While albite (NaAlSi 3 O 8 ; approximately a mass fraction of 8 % Na) represents a typical choice for some microanalysts, it may be subject to time dependent signal intensity issues, such as those observed for Na and other cations during analysis of hydrous glasses [ 2 ]. Near endmember jadeite pyroxene (NaAlSi 2 O 6 ; approximately mass fraction of 11 % Na) represents a desirable option for calibration given its relatively large concentration of Na and insensitivity to electron beam radiation with respect to X-ray output. Despite these desirable characteristics, jadeites have been shown to contain complex microstructures as the result of intracrystalline zoning [ 3 , 4 ], and the impact of chemical inhomogeneity within mineral standards and natural glasses has been documented [ 5-7 ]. In this study, a commercially obtained jadeite crystal (source location “China”) was studied to assess its microscale uniformity using a suite of microbeam methods, including dispersive red-green-blue multispectral cathodoluminescence imaging (CL RGB ), hyperspectral CL imaging spectrometry, energy dispersive X-ray spectrometry (EDS), SEM-based micro-X-ray fluorescence (μXRF), and wavelength dispersive X-ray spectrometry (WDS).

Microscopy and Microanalysis↗

USGS2021

Mismatch-induced growth reductions in a clade of Arctic-breeding shorebirds are rarely mitigated by increasing temperatures

In seasonal environments subject to climate change, organisms typically show phenological changes. As these changes are usually stronger in organisms at lower trophic levels than those at higher trophic levels, mismatches between consumers and their prey may occur during the consumers’ reproduction period. While in some species a trophic mismatch induces reductions in offspring growth, this is not always the case. This variation may be caused by the relative strength of the mismatch, or by mitigating factors like increased temperature-reducing energetic costs. We investigated the response of chick growth rate to arthropod abundance and temperature for six populations of ecologically similar shorebirds breeding in the Arctic and sub-Arctic (four subspecies of Red Knot Calidris canutus , Great Knot C . tenuirostris and Surfbird C . virgata ). In general, chicks experienced growth benefits (measured as a condition index) when hatching before the seasonal peak in arthropod abundance, and growth reductions when hatching after the peak. The moment in the season at which growth reductions occurred varied between populations, likely depending on whether food was limiting growth before or after the peak. Higher temperatures led to faster growth on average, but could only compensate for increasing trophic mismatch for the population experiencing the coldest conditions. We did not find changes in the timing of peaks in arthropod availability across the study years, possibly because our series of observations was relatively short; timing of hatching displayed no change over the years either. Our results suggest that a trend in trophic mismatches may not yet be evident; however, we show Arctic-breeding shorebirds to be vulnerable to this phenomenon and vulnerability to depend on seasonal prey dynamics.

Global Change Biology↗