Mineral Composition And Structure Studies Of Dumoriterite Quartzites In Peru

Dumortierite is an unusual aluminium boro-silicate mineral and the mostabundant mineralogical sink for B after tourmaline. It typically consists of radiactingfibres or acicular aggregates. There are few dumortierite mineral resources in theworld, especially the single crystal. Systematic research has a great significance inmineralogical and Gemology characterastic for dumortierite in Peru.Dumortierite quartzites in Peru were studied in this investigation. Researcheshave been conducted on mineral composition and structure characters using modernmethods including the Polarzing microscope, scanning electron microscopy, electronmicroprobe, XRD and IR spectrum, etc.The result of microscopic observations and XRD analysis revealed that thedumortierite quartzites from Peru were mainly consist of quart,dumortierite,pyrophyllite and Kaoline，Quartz is mainly round to irregular angular. Inaddition,the crystallinity indexes of quartz is6.55~8.91, has a high degree of orderand a strong metamorphism. The surface morphology observed by SEM showed:dumortierite commonly forming bundles, needles fibrous aggregates with a radialtexture. Dumortierite nodules are0.2~2μm in diameter and5~10μm length. It isfibers of aggregates. The texture shows dumortierites are closely associated withpryphyllite, which often symbiotic with pryophyllite and through the boundary gap inquartz.The result of Electron microprobe for the dumortierite quartizites in Perurevealed that the chemical composition of Al2O3is lower than thoretical value andSiO2is higher than standard value. ω(Al2O3) ranges from55.71%to60.96%andω(SiO2) ranges from33.88%to39.27%, suggesting a trend of increasing silicificationand a decreasing trend of Al activity. The structural formula of dumortierite isrecalculated as：Al6.00(Al0.34Mg0.01Ti0.01Fe2+0.36Mn0.01Ca0.03)(Si3.2O12)B1.02O3O3.The result of infrared spectrum of the dumortierite quartizite were gainedmainly from the vibration mode and frequency of water,[BO3] triangle.[BO3] group has three vibration mode: The absorption band at1435cm-1related with thevibration of the B-O-B asymmetric stretching bands, The absorption band at949cm-1related with the vibration of the B-O-B symmetric stretching bands, Theabsorption band at693cm-1is related with the vibration of the B-O-B symmetricstretching bands. In the dumortierite of this study, The vibration of OH stretchingband at3675cm-1、3496cm-1、3620cm-1investigated that dumortierite has structureof water.By differential thermal analysis, the samples have a strong and sharp valley at676.64cm-1, water loss between450℃~600℃, indicating occurrance ofdehydration. the crystal structure has changed, indicating the presence of OH inpyrophyllite, the Department of lose structural water effects.The blue is primarily related to the dumortierite indumortierite quartize in Peru,combined the X-ray energy apectrum and UV-VIS show the mainly elementsFe2+、Ti4+lead to its colour，the colour can be attributed to Fe2+–Ti4+charge transfer.