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This study aims to compare iso-rank vitrinite-rich and inertinite-rich coal samples to understand the impact of coal-forming processes on pyrolysis chemistry. A medium rank C bituminous coal was density-fractionated to create a vitrinite-rich and an inertinite-rich sub-sample. The vitrinite-rich sample has 83 vol% total vitrinite (mineral-matter-free basis), whereas the inertinite-rich counterpart has 66 vol% total inertinite. The vitrinite-rich sample is dominated by collotelinite and collodetrinite. Fusinite, semifusinite, and inertodetrinite are the main macerals of the inertinite-rich sample. Molecular chemistry was assessed using a pyrolysis gas chromatograph (py-GC) equipped with a thermal desorption unit coupled to a time of flight mass spectrometer (MS) (py-GC/MS) and solid-state nuclear magnetic resonance (13C CP-MAS SS NMR). The pyrolysis products of the coal samples are generally similar, comprised of low and high molecular weight alkanes, alkylbenzenes, alkylphenols, and alkyl-subtituted polycyclic aromatic hydrocarbons, although the vitrinite-rich sample is chemically more diverse. The lack of diversity exhibited by the inertinite-rich sample upon pyrolysis may be interpreted to suggest that major components were heated in their geologic history. Based on the 13C CP-MAS SS NMR analysis, the inertinite-rich sample has a greater fraction of phenolics, reflected in the py-GC/MS results as substituted and unsubstituted derivatives. The greater abundance of phenolics for the inertinite-rich sample may suggest a fire-related origin for the dominant macerals of this sample. The C2-alkylbenzene isomers (p-xylene and o-xylene) were detected in the pyrolysis products for the vitrinite-rich and inertinite-rich samples, though more abundant in the former. The presence of these in both samples likely reflects common source vegetation for the dominant vitrinite and inertinite macerals. [ABSTRACT FROM AUTHOR]

Clinopyroxene megacrysts (up to 5 cm) from a scoria cone on Marion Island, Antarctic Ocean are zoned, with compositionally distinct low (Al + Ti) and high (Al + Ti) patches arranged haphazardly throughout crystals. Inclusions of olivine, pyrrhotite, oxides, sulphides, and rounded inclusions with euhedral micro-crystals interpreted as former melt inclusions are observed. Olivine inclusions have variable compositions, ranging from primary Ti-poor crystals to Ti-rich crystals hosting secondary haematite crystals formed by hydrogenation. The crystals contain voids that are concentrated in the middle of each crystal indicating that the initial crystal growth was skeletal. Subsequent crystallisation filled in the skeletal framework creating the patchy zoning in the crystals. The Marion Island megacrysts are not homogenous, but the combination of crustal clinopyroxene compositions, primary and hydrogenated olivine, and the mode of eruption in scoria eruptions indicates that these crystals most likely formed in a shallow magma chamber. Primary olivines crystallised from a mafic magma and secondary altered olivines were incorporated into a rapidly growing megacryst in a super-saturated, fluid-rich environment, prior to being ejected onto surface in a scoria eruption. [ABSTRACT FROM AUTHOR]

Coal contains a significant concentration of free radicals as a result of the coalification process. One of the experimental methods sensitive to the presence of radicals is electron spin resonance (ESR), and differences in ESR spectra for different macerals may provide insight into coal-forming processes. In this study, ESR data along with the H/C atomic ratio (to infer the aromatic fraction) are used to characterize coal samples with the aim of assessing a fire-origin for dominant inertinite macerals. A medium rank C bituminous Witbank No. 4 Seam Upper coal (the parent) was density-fractionated to create vitrinite-rich and inertinite-rich samples. The parent sample consists of 42 vol% vitrinite and 49 vol% inertinite. The density-fractionated samples comprise of 81 vol% total vitrinite (dominated by collotelinite and collodetrinite), and 63 vol% total inertinite (dominated by fusinite, semifusinite, and inertodetrinite). The H/C ratio is 0.74 for the inertinite-rich sample, and 0.85 for the vitrinite-rich counterpart, suggesting the former sample is more aromatic. The ESR spectra obtained for the three samples were found to fit best using a Lorentzian distribution. The fit is noticeably better for the aromatic inertinite-rich sample, for which the spectrum is symmetric. This is attributed to pronounced electron mobility and exchange interactions. The higher radical content of the inertinite-rich and parent samples is attributed to the presence of specific inertinite macerals, namely: fusinite, semifusinite, and inertodetrinite. And, owing to the greater radical content of the inertinite-rich sample, the dominant inertinite macerals are interpreted to have formed through charring of plant matter. [ABSTRACT FROM AUTHOR]

We as the authors of the article "Clinopyroxene megacrysts from Marion Island, Antarctic Ocean: evidence for a late stage shallow origin" (Roberts et al. [1]) gratefully accept the constructive Comment received from Dr. Hedding. In our private discussions with Dr. Hedding, he noted that the clinopyroxene scoria cones are much rarer than we had believed, and that only Pyroxene Kop consists primarily of clinopyroxene megacrysts. Clinopyroxene megacrysts from Marion Island, Antarctic Ocean: evidence for a late stage shallow origin. [Extracted from the article]