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Opal: SiO2·n(H2O) Todorokite: (Na,Ca,K)2(Mn++++,Mn+++)6O12·3-4.5(H2O)
Comments: Dendritic todorokite in white opal. Location: Brosso Mine, Ivrea, Torino, Piemonte, Italy. Scale: See Photo. © Jeff Weissman / Photographic Guide to Mineral Species
Opal: SiO2·n(H2O)
Comments: Colorful white opal on a sandstone matrix. Location: Queensland, Australia. Scale: 9 x 6 x 3 cm. © Isaias Casanova / IC Minerals
Comments: Section of fossilized tree limb that is now completely replaced by black opal. Location: Virgin Valley District, Humboldt Co., Nevada, USA. Scale: 20x13x11 mm. © John Betts - Fine Minerals