Green Opalised Wood from West Java, Indonesia.

This study describes a rare type of green opalised wood that was recently discovered in the Garut region of West Java, Indonesia. Multi-scale structural and chemical analyses (XRD, Raman, SEM and TEM) revealed that it consists primarily of opal-CT. The unusual green colour of this material is attributed to the presence of micrometre- to nanometre-scale inclusions of glauconite/celadonite dispersed throughout the opal matrix. The green colour likely originates from Fe²+-Fe3+ charge transfer and Fe d-d transitions within these inclusions. The green UV luminescence of the material, related to uranyl groups, is surprisingly vivid despite the presence of Fe (which usually quenches luminescence), because most of the Fe is segregated in the glauconite/celadonite inclusions. The luminescence and geochemical signatures identified in this study, along with the published literature on the region of origin, suggests a formation process involving intense continental weathering and leaching of volcanic soils during Pliocene-Quaternary time. [ABSTRACT FROM AUTHOR]