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Studies of chrysoprase and microcrystalline silica varieties from serpentinites of Szklary Massif (Foresudetic Block, SW Poland) by Raman spectroscopic technique – preliminary results

Korybska-Sadło I.

Mining Science

2015

Vol. 22, Special Issue 2

39--45

The mineralogical properties of green colored chalcedony varieties from weathering cover of slightly serpentinized peridotites (harzburgites) occurring near Szklary village on Foresudetic Block (SW Poland) are studied using Raman spectroscopy in the 200 – 1600-1 wavenumber region . The obtained results show, that in examined samples, the peaks like: 206, 265, 355, 394, 464, 696, 796, 808 cm-1, characteristic for α-quartz were ascertained. In one sample, the characteristic moganite peak (502 cm-1) was found. It implies that presence of other polymorphs of SiO2 in crystalline structure, considered a proof for presence of moganite intergrowths with α-quartz. It indicate, that intensity of green color of measured samples of chrysoprase are not correlated with Raman spectroscopic data. It can be conclude, that examination of Raman spectra can be useful only to recognition of internal phase composition of green cryptocrystalline silica polymorphs occurring in weathering cover of serpentinized peridotites.

The fossil wood of East Cairo, Egypt: A mineralogical view

Hassan K. M.

Mineralogia

2014

Vol. 45, iss. 1/2

47--57

As part of the characterization of the petrified wood of East Cairo at the New Cairo Petrified Forest, representative samples collected from the area were studied by X-ray powder diffraction (XRD) and optical microscopy. The samples, as indicated by XRD analysis, are composed of quartz ± some goethite ± minor moganite ± minor gypsum ± trace calcite. The absence of moganite in some samples has been attributed to the transformation of moganite to quartz or to leaching processes. Under the optical microscope, some of the 10 petrified-wood samples are permineralized with mainly microcrystalline quartz (chalcedony), some with a combination of chalcedony and microgranular quartz, and some with microgranular quartz. The sequence of silicification is likely to have been either opaline precursor to chalcedony and quartz, or directly to chalcedony and quartz. The crystallinity indices (C.I.) of the quartz in the samples studied, measured using a standard X-ray powder diffraction procedure, are consistent with the petrographic finding.