![]() This was also observed for a similar compound spherulite in another specimen (Specimen #2, Sample #2a). I should note that this sample required powder grinding with corundum (Mohs 9+), and that this type of compound spherulite is the hardest of the surrounding material. Only a subset of natural chalcedony samples shows intergrown moganite characteristics. These additional weak reflections indicating intergrown moganite were not observed in any of the XRDs of samples in this characterization study, including Sample #1a. It is known that moganite has a structure that can be described as an alternate stacking of left- and right-handed quartz, and can be found intergrown with chalcedony at the twin boundaries this phase is observed in some samples of chalcedony that under high resolution imaging show length-slow fibrous growth. 3a does not show characteristic SiO2 polymorph moganite peak reflections seen in some samples of chalcedony – these are weak reflections at d-spacings 4.46Å (20.0°), 3.09Å (28.6°) and 2.91Å (31.0°). The smaller relative intensities of the secondary peak (4.23Å) and tertiary peak (1.82Å) compared to ideal alpha-quartz are such an indication. The sharp peaks in the XRD (Fig.3a) with minimal background but slightly broadened (FWHM) peaks over ideal alpha-quartz indicate an ordered microcrystalline chalcedony. Since the XRD for chalcedony is almost identical to that of SiO2 quartz, the XRD characterization (Fig.3a) indicates chalcedony, given that past optical microscopy of spherulites in this material show fibrous microcrystalline SiO2 (chalcedony) growth of spherulites, though I submit that further imaging characterization should be done on these specimen samples via high-resolution SEM and transmission electron microscopy (TEM), to verify detailed growth characteristics of the spherulites vs. The results show that the orbicular “bullseye” spherulite sample (Sample #1a) is silica quartz (SiO2), no other appreciable elements or minerals present (Figs.2a&3a) other than a trace amount of iron (Fe) that contributes to the color. ( Note: Right click on Figure links to open figures in new window) Sample #1a Fig.1: Specimen #1 - Front Fig.1: Specimen #1 - Front-Left Fig.1: Specimen #1 - Side Fig.1: Specimen #1 - Bottom All three samples were tested by both EDS (Fig.2) and XRD (Fig.3). Three samples were tested from the areas marked in the specimen photos (Fig.1). The specimen has an outer “rind” of weathered material along the bottom edge and crystalline quartz druzy along the top edge. The first specimen is a thick slabbed chunk of ultra-rare old stock Ocean Jasper from off-shore, underground Marovato mines (estimated mining period 2001-2003) with large “bullseye” and compound semi-translucent spherulites in a mixed color semi-translucent chalcedony matrix. Crystallography tests reported were done by powder x-ray diffraction (XRD) using standard copper Kα radiation diffractometry. Ĭompositional tests reported in this article were done by qualitative energy dispersive x-ray spectroscopy (EDS) via scanning electron microscopy (SEM) using a Cambridge S100 SEM, a XR-100-CR pin diode detector and DTSA software, 25 Kev accelerating voltage. Feature descriptions, grade classifications, large-format specimen photos, and an extensive discussion of geological information and possible formation are discussed in. ![]() The rarer high-grade varieties are “old stock”, mined between 2001-2006, mines depleted and no publicly known similar quality veins found since. Ocean Jasper is a rare orbicular rock uniquely from Madagascar, classified as a “spherulitic chalcedony”. I provide an analysis of the results and I identify a series of next-step characterization tests. ![]() In this article I present the first known compositional (SEM/EDS) and crystallographic (XRD) characterization studies for 7 specimens of old stock Ocean Jasper. ![]() Characterization Studies of Ocean Jasper Author: Susanne Lomatch*
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