| Popis: |
Common opal comes in a variety of colors including green, orange, red, yellow, and white. The specific gravity of the samples ranges from 1.83 to 1.95. The refractive index ranges from 1.44 to 1.45. According to the Fourier-transform infrared results, the absorption bands ranging from 4000 to 400 cm-1 are related to lattice vibration. There are absorption bands at 3400, 1630, 1095, 793, 621, and 479 cm-1 . The results of X-ray diffraction used to identify and/or characterize crystal structure indicate identification as opal-CT. To determine the nature of chemical impurities, samples were analyzed using inductively coupled plasma - mass spectrometry after dilution. The results are related to the mode of formation and physical properties, and they help to define the geographical origin. Rock samples are silicic in composition and show a sub-alkaline magma series, whereas volcanic rock samples are rhyolite. The REE patterns of opals and rocks are parallel. As a result, the opals are genetically related to their host rocks. The Ba content is critical in distinguishing volcanic opal from sedimentary opal. Because the Ba level is below 110 ppm, the sample is from a volcanic environment. |
