La moganita, una nueva perspectiva en el estudio de rocas de la sílice

Moganite (formerly SiO,-C) is a novel monoclinic silica polymorph and it is a widespread distribution component in microcrystalline silica rocks. The identification of moganite in the presence of a large proportion of quartz is difficult by microscopy or other usual mineralogica! methods. Rieltveld refinements of powder X-ray diffraction ora position-sensitive detector system allows identification and quantification by XRD. Raman analysis also provides a measure of moganite content and the micro-Raman permit to know their spatial variation in the microcrystalline textures. The results obtained indicate that moganite occurs as a metastable phase that transforms to quartz, if sufficient time or a change in ambient conditions are produced. Then, the general diagenetic sequence of the silica rocks up to now known (opal A-*opal CT->Quartz) must be revised because moganite is part of the opaline maturation sequence. The moganite is abundant in arid environments and it is likely due to the lack of water available to support the dissolution of moganite and simultaneous precipitation of quartz. More data about the moganite in evaporitic environment may determine special kind of sulphate or alkaline environments.